Sudoku: The Only Mind Virus You Need!

thank you hello and welcome to Monday's edition of cracking the cryptic where no I I'm not Tipsy today I'm actually starting this video earlier than usual because I'm anticipating this could be a long one I'm going to have a crack at chaos cave Sudoku by Magnus Josephson now Magnus is one of the very tip top solvers and Setters in the whole world uh the brother of Jasper Josephson I think they're twins if I remember rightly so what an intelligent family Jesper Josephson is another total genius who we've covered on the channel many times but the reason that I feel I have to have a go at this even though it's an incredibly large grid is it's got a 100 approval rating on logic Masters Germany five stars out of five for difficulty and the comments from those who have managed to solve it and there aren't that many are Stella it's been recommended to us requested by those who have failed to solve it as well so I am going to have a go at it for you um but I I imagine this is going to be a brutal puzzle um and it's sort of a I think I've done hijavu because I think Magnus did another type of puzzle that was similar to this that was it might have been called cave phenomena Sudoku and maybe it was no maybe it wasn't Sudoku maybe it was just phenomenal logic with cave logic I I don't know I'm getting that that sort of feeling that I've seen something like this before um but it's got an absolutely remarkable rule set we actually have to find where in this grid there is a hidden Sudoku grid um yes that doesn't look very easy to do does it anyway that's that's going to be our task um in a moment or two let me uh what can I tell you about before that let me first of all show you the weather that we've been grappling with um and can I show you this actually yes I can look here there that is the crack in the cryptic Garden this morning full of snow this doesn't happen very often in the UK it's very beautiful uh but quite difficult when driving let me tell you that anyway I thought I'd share that with you um what else did I need to tell you about there was loads of stuff I was meant to mention I'll do the birthdays happy birthday Sally from your sister Anne um I think Sally you're over there in Arlington Virginia and Ann's in Boston and I understand that you you spend quite a lot of online time talking about the puzzles on the channel which is lovely I love hearing about how families have been brought closer together um by these puzzles it's absolutely brilliant phenomenon um and also Daniel you've turned 26 today and Daniel I appreciated your hopes that The Echoes of the chocolate cake you were planning to have would waft their way across the pond um I hope so too but I I live in Hope if not expectation um other than that we've got of course we've got the cryptic scriptures of The Secret Snake Society this is our patreon reward um because because I was out yesterday I haven't had a chance to finish the final Festival puzzle that we're hoping to release as a Christmas present to our patrons but anyway there is of course this massive um snake hunt for you and very well done to the following who've managed to solve all of the puzzles in that hunt somebody palfly camping Hunter John growthar arachnothera Titus adaxis um Darko image Dave Mustang Lang um Matt bernardina Rob Driscoll Peter spute Benoit massart Scott Abercrombie naresh satyan and Kim Geiger that is the next batch of names very well done to all of you you've still got a week more than a week to enter the competition and if anybody manages to finish all the puzzles then they'll get a shout out on the channel so do get cracking and if you do start and you get stuck go over to the patreon channel on the Discord server there's loads of help available there anyway we should delay no longer because this could be about a six hour video let me read you the rules of chaos cave Sudoku by Magnus Josephson they are as follows and I've got oh hang on I've got an example puzzle that I just snipped from logit Masters Germany where is that because we are going to be thinking about this so this is a completed grid although you can see the completed Grid in this puzzle is a six by six Sudoku osc well it yes it is a six by six Sudoku but it's sort of oh hang on let's read the rules find out what's going on Place some digits in the grid and shade some cells so that a there is a nine by nine subgrid filled with digits that forms a valid standard Sudoku right so in this example I think there's a six by six Grid in the middle of the Grid it's it's framed in blue it's not the white cells there's something different B disregarding oh okay so disregarding the interior 7x7 of the Sudoku subgrid the rest of the grid forms a valid cave and we're going to talk about what that means in a moment I think so let's look at this example in the example there is a six by six that's been hidden in the puzzle and we can see that then you ignore the sort of middle bit of the six by six which is the white cells and the rest of the grid has to form a valid cave now what is a valid cave a valid cave is formed where all unshaded cells are orthogonally connected right so that must be the green cells yes I can see all the green cells they are all orthogonally connected that is true okay um all shaded cells are orthogonally connected to an edge of the grid NB the borders around the 7x7 interior of the Sudoku are edges for this purpose right oh so what's that saying that's saying that the gray cells have to connect to an edge and it looks like they do doesn't it I see so sometimes so like in this sixth region they connect to two edges because they connect to the bottom edge of the grid and the sort of edge of the white which is to be treated as an edge for the purposes of these rules This is complicated um okay but I think I understand it so far now what's the rest of this I could have to scroll down then I'll I'll reinstate the example puzzle so are each number written in an unshaded cell must show how many cells can be seen from that position horizontally and vertically where the view is limited by the next shaded cell or an etch of the grid the cell with the number itself is included in the count and each number in a shaded cell must equal the total number of shaded cells in that orthogonally connected group of shaded cells good grief wow wow I can see why this is five out five differently it's five out of five difficulty to understand the instructions so let's just think about this so I can see if I look at the gray areas and see where they have a digit in them those gray digits seem to be specifying the size of the island that they are in not all gray areas actually have a a number in them but that's two for example here you can see that's part of a region of size two this six is part of a region of size six but oh that's Mark calling um but I'm going to carry on um so but let's just think about the green regions because the green regions have icy so the green regions operate like normal cave rules so this six here let's look at this six that I'm just ringing here you can see that if you count how many green cells it sees as sort of an e in an East-West Direction it sees four including itself and then a north-south direction it sees two more so it sees six altogether this five sees the same four horizontally that the six C's and then it sees one cell in the north X1 extra cell in the north-south direction that's why it is a five right but the challenge here I can immediately see is going to be to understand how we shade the puzzle because it it if we go back to this puzzle which is our actual puzzle which is an enormous grid let's actually see one two three four five five six seven eight nine ten eleven twelve thirteen right it's 16 across is it it does look Square so it's probably 16 by 16. but we don't know any of the shading I mean imagine we knew this four was shaded then we would know that it has to connect to the N or an edge of the grid which could be this Edge or it could be the edge of a Sudoku grid we're going to have to find in the puzzle called grief This is complicated right anyway do have a go the way to play is to click the link under the video I fully appreciate that this is this is complicated today but it is meant to be a spectacular puzzle and I will tell you that Magnus is a spectacular Setter we are dealing with a spectacular mind today so if you want to do battle with a spectacular mind I can think of no better way to do it than to spend some time today thinking about this puzzle now if you don't mind who I am going to spend a moment or two um the way to play of course is to click the link under the video I can't remember if I said that now I'm going to play Let's get cracking but rarely for me I'm going to start getting cracking by staring at the example grid again and just trying to understand what it is anything that is constraining the puzzle so what I'm what I'm sort of thinking about here right I have actually spotted something as a result of looking at this grid so this was not not a Fool's errand ah but the problem is right one's in the grid well this is the difficulty is you don't know where the Sudoku is but you can I can see that ones in the cave area of the grid are always shaded and that makes sense because obviously imagine this one here was unshaded that would be saying that it would be a green cell so one would be the count of the cell seen in the in the east west and the north south directions so it would only see itself so it would be isolated it would be surrounded in fact by gray and that would break the rules of the puzzle which requires the greens to all be orthogonally connected to each other so if we can find all right let's go back to this grid we've got we've got four ones that are given let me move my pencil if we've got four ones that are given if well it's not possible for those two for example to be both in the Sudoku grid so one of those at least must be gray and if it's gray wow wow if that I've just had another thought if that was Gray how would it connect to the edge of the grid it would have to connect to the edge of the Sudoku grid wow although the other alternative of course is that this is great no hang on which way around is it yeah so if that's gray that can be part of the Sudoku grid no hang on it's on the period oh now I'm getting really confused let's go back to the example everything yeah ah okay so actually a one if we look at ones on the perimeter well look at this one that's gray and even if I if I I push the Sudoku grid left in this puzzle um because the perimeter of the Sudoku grid is always counted both in the Sudoku and in the cave part of the puzzle a one in the perimeter will always be well you can't have a one in the puzzle oh well you can't have a one on the perimeter of this puzzle by which I mean the Outer Perimeter that is not a cave clue it could be part of the Sudoku so this could be part of the Sudoku but even if it is part of the stoku it has to be a cave clue because imagine we put a 9x9 in the corner like something like that I might have got the count wrong it doesn't matter but if that's the 9x9 um we we know that the bit of the nine by nine that doesn't count in the cave I think I think I've done this eight by eight actually but the point is uh in fact I will fix it because it might confuse people um so let me make it slightly bigger there we go so this whole area here is the Sudoku everything that is blue and the green interior which is agree the green interior 7x7 would not count as part of the cave as well so but this one clue the point is this one clue would always be part of the cave so although hang on I'm now worrying that you could never have I'm wondering now whether you can ever put the Sudoku grid this close to the edge because now this is nonsense I I well I'm going to claim that this is total nonsense I don't think this is so I don't think this is a possible Sudoku grid and I don't think any I'm going to make a further claim which is that I don't believe it's possible to ever put the Sudoku Grid in this 16 by 16 Grid in a position where it borders the puzzle where it borders on the 16 by 16 perimeter and that's because let's just look at this this bottom bit here I'd have to fill obviously I've got to fill the bottom of the grid with some numbers it doesn't I don't think it's going to matter what these numbers are let's just put some in these all have to be valid cave Clues well that only one of these that now this is wrong this never works yeah this is good actually this is a good deduction so the only clue you could ever put that bounded the seven by seven uh as a gray clue would be the one because the one can be gray because it is in an island of size one and it can be surrounded by Green on these two sides but how could this be a gray six clue that would be saying it was in an island of size six but the green doesn't count towards this island so that I'd have to I'd have to spread it to touch so this sit if this six was Gray it's going to have to cut touch and make gray other cells that are adjacent to it and that immediately contradicts it because this is this six is saying if it's great saying it's in an island of size six so we try and make an island of size six and it immediately touches a five makes that gray and that says oh no this is this six is actually in an island a size five which is contradictory so the only way this could work every digit apart from the one along a boundary would have to be green but that doesn't work because if we make these green what cells are they seeing well they're seeing everything horizontally but they're not seeing anything vertically green is a terrible color for this interior I've just realized um yeah I shouldn't have made the screen that's going to confuse people let me just change the color of this interior bit just so that there's no confusion here about what about what I speak uh it's got to be blue uh oh I should have ungreened this bit first but I didn't um there right so these would all be green but what are they seeing well they're they can they can't see anything North they're blocked by the edge of the grid as defined by the inner Sudoku grid so they have to see horizontally and if they see horizontally they're all seeing the same count of cells they're seeing however many horizontally that are green so they all should have the same clue and they don't so this is important this is important because now well I might as well reset the puzzle actually I'm just going to restart it now not only am I convinced that this cell is gray and this cell is gray I'm further convinced that neither of these cells is part of the actual Sudoku a nor indeed is any any cell on the perimeter I'm wondering if it's worth coloring that but I think I'm going to get confused if I color that I think I'm just going to remember that none of those cells that I've just highlighted let me highlight them briefly none of those purple cells is part of the sudoku for the reasons I've just explained now what does that mean I don't know but what I am going to do because I've learned that these ones are definitely shaded I'm going to surround them with unshaded cells that are part of the cave now now do you get the checkerboarding in this puzzle that you normally get in cave so I'm looking at this one my answer is hang on this is where I'm gonna have to pause and use my brain and e by gum what does that mean as I think I'm just gonna think about this up here if that's all right so normally in a cave puzzle that pattern shading is impossible and let me explain why it's impossible because we have two contradictory conditions that we need to fulfill the first condition is that every Gray area gets to the edge of the grid the second condition is that the green areas connect with one another orthogonally so you can see that to connect the greens up if we decide the greens are going to connect down this way however they do that whatever pattern they achieve this connection by however circuitous it is this gray could never get to the boundary if they decide on the other hand we're going to connect these greens around the top we have exactly the same problem this gray can never get to the boundary now what I'm just wondering is does that apply in a puzzle where there is an internal boundary I have no clue let uh let's just draw in well it doesn't have to be a big grid I'm just going to draw in a little grid just let's put in a mid so we're going to put this little Sudoku Grid in the middle of the thing where where we're saying that anything that touches blue not not purple anything that touches blue orthogonally is treated as having achieved touching an edge so imagine that six was Gray and it did that then this six has touched a boundary let's make it six so it doesn't it doesn't affect my OCD um now does that does that make any difference at all I haven't I don't know sorry I can't quite visualize this um I apologize to everyone out there who's shouting at me now does it make any difference if you can have an internal I can't see it I'm struggling to see it sorry um or maybe or okay so maybe it's okay let me think about it I'm actually not going to I mean I think this six is confusing me I'm gonna get rid of that I'm just gonna put a checkerboard in here right let me think about this so why would this either be possible or impossible normally we would say it was impossible because ah right no this is now this is very annoying this now is possible I can now see it but now I've got away from my six inch here but because what if this cell touched this two by two like that for example now ordinarily in without this Central the ability to get hold of an edge in the middle of the grid we would have said okay well if we connect these greens around the top this would have been isolated from an edge and that work can see it would be isolated from an edge except that there's an internal edge here in blue so if the green Rings the whole Sudoku grid like this foreign you rotten thing oh dear oh dear that's very annoying that's very annoying so you can in this puzzle so let me just stare at this for a bit longer so in this puzzle all my normal cave restriction doesn't even apply this is so annoying because what I wanted to do is make both of those cells green and now I don't even think I can do that yeah because imagine in fact imagine that cell when did its way somehow and managed to touch that blue cell there I suppose it can't one two three four five six well I mean this this is a silly example but I was just thinking this this can't it can't touch it with an island that's bigger than size nine oh no it can oh no that's that's a nightmare as well I've just realized I might not even have the digits to do this puzzle oh my uh although hang on if it touches that if it touches the Sudoku grid yeah no actually that I think there is a restriction I think the maximum checkerboard avoiding Singh would be nine because it would have to connect it has if you've got to connect it orthogonally to here it's going through the perimeter of the Sudoku which means there's got to be a gray 9 as a maximum digit here so maybe if this was the grid this that wouldn't be possible in this particular example because it would take more than nine orthogonal steps to get from here to here but of course this doesn't need to be the Sudoku grid the Sudoku grid could be much closer to this cell so right so this this joins the Sudoku grid Let's ignore the nine restriction for a moment but then this green and this green can Loop right around the Sudoku grid and that would be fine ah although okay there is at the right here is another point then here is another point that might not be true and that's why I'm pausing it I'm just trying to think about it this is the question I'm asking in my brain um and my brain is not telling me the answer but I'm suspicious the answer I know the answer um can you have two checkerboards in this puzzle is a question I want to ask and the answer to that might be no because I was just thinking about this this checkerboard here if we if we sort of play this out this cell has to get to an edge but because we needed to connect the greens around the whole Sudoku grid the only way this gets to an edge if it goes to an edge of the actual grid because it can't cut through this this this orthogonal connection which is necessary between these two green cells so imagine we're in this situation and then we give ourselves we set ourselves the task of having another checkerboard in the puzzle so we've got this one that's a checkerboard can we put another one in now and I'm going to claim the answer is no and the reason I think it's no is that in effect I think it is no and the re the reason I think it's no is that this pattern here forms in effect a wall and a wall that an orthogonal connection of green can never breach so if there was another checkerboard let's put it up here um let's put it up here let's go then how would we do this we we know that the only way that this can work is if this connects to the middle of the grid which it can do although although that would in oh actually I could put it inside out good grief right to actually make this General I think I've got to put it inside this connection so I'm going to do that um let's put it in these cells foreign there so this is the one I want to focus on now that one now how would we do this well connect this to the interior that would work to do that but now we know that this must connect to the edge of the grid let's make that happen now you can see it's already giving us a problem which is that these in order to connect this and this together the point is that you have to you have to ring this and in ringing that you're going to run into this wall so that is impossible so you can have one checkerboard and that's that's General that must generally be the the case mustn't it because in allowing yourself the luxury of one checkerboard you are basically creating a wall from the 7x7 interior Sudoku grid to the external perimeter which another orthogonal connection of greens around around that internal Sudoku grid cannot breach and therefore at that point we would go back to the normal cave secret which is you can't have a checkerboard right and the problem with all this is it's all utterly utterly relevant in fact in terms of solving the puzzle because well I can keep these everything everything internal to this is gibberish because it's just it was just as an example to make me understand the puzzle and more importantly let's get rid of my lines here as well I cannot now even green those two cells yeah if I'd been able to Green that I would have broken the puzzle oh hang on a moment what's going on there then now I'm confused um well I can uh sorry I know I've just stopped speaking that's because I'm now worried that everything I've just said is about well I thought I was going to be able to well if I'd so is this is this a checkerboard then is what I'm now thinking that would be really beautiful if if this is if this is I really like this if this is right because it's actually falls out of some very natural logic what oh it's looking down here and I was thinking if you couldn't have a checkerboard I was going to be able to create a new pentomino of greenliness around here I didn't notice that this one has a 2 in this position so I was hoping obviously to go double green to avoid checkerboards but it just occurs to me now how can that ever be green if that's green I could buy this if there's a Sudoku somewhere near I don't think so oh no that might be it okay yeah okay I've suddenly had a horrible thought about this I have been flippantly making these two cells green I mean what we can say what we can say is if if the Sudoku grid doesn't interfere with this six cell sequence if there's no Sudoku grid near here say the Sudoku grid is over there somewhere then that then there is no way this this cell here can be green because if it's green and part of the cave it's definitely seeing three cells so that cell would have to be Gray and that creates a checkerboard and that gray would have to get to the Sudoku grid in on the interior so that would be a massive deduction that would be a massive deduction if that's true but I don't think it is well it could be true but I don't think it's necessarily true because what I think I've missed here is is it actually the case that I can I can shade the interior is it necessarily the case that this cell is part of the cave it's certainly true these two have to be because we did the work earlier on discovering that the perimeter of the puzzle is entirely not in the Sudoku but why is that cell not in the Sudoku is the question I've got for myself unfortunately so let's just put the Sudoku here somehow one two three four five six seven eight nine um trying not to sneeze right let's say that's the Sudoku oh hang on if that's the Sudoku that still is green oh no it's this is okay this is okay I'm being I'm being very slow yeah no no it's fine I was just I miss I'm getting myself confused in my head between the internal 7x7 and the total nine by nine now okay so let's let's let me let me re-explain to myself now not to you guys who will be all over this and I'm just being slow but I proved in my own mind that you couldn't have the Sudoku doing this that's impossible so the closest the Sudoku ever gets to the edge is something like this but that's important for the one clue because those cells even in that situation are still in the perimeter of the Sudoku and therefore count in a cave so it is valid to do that and that now if that's true and this can't be green that has to be actually a real gray too and create a real checkerboard so now What on earth does that mean because to connect this and this together which I must do you can see this well it's not big enough anyway but if this somehow got to the edge like this this screen would be isolated so that's not doing that this cell is connecting either is connecting to the seven by seven yeah it's just because it's now this is really confusing let I'm going to come back to the example it's the seven by seven that's providing the edge of the grid that allows a checkerboard to happen so this too either in this cell or this cell is hitting the seven by seven interior of the puzzle that cannot happen I don't think that this is ah this is really clever I think this has been positioned such that it literally cannot create a Sudoku grid downwards let me just let me just think about this um I know that the Sudoku grid cannot run along here so the closest one two three four five six seven eight so that is if so if the gray goes downwards it would have to look something like that no but that's running along the bottom again that doesn't work I'm not allowed to do that so I'd have to go up again one two three four five six seven eight nine and then I'm just gonna make this blue for a moment let me just think about this so what's wrong with that I haven't got a clue um oh no this doesn't right oh that's lovely oh this is rare it's really all the deductions are findable actually it's just getting your head around it and I'm being really slow I've taken 38 minutes to do nothing here but I'm getting there now because no this does not work and the reason it doesn't work is the only way that this sort of thing the only way this this can come downwards for its its second connection is if if is if this is running along the nine by nine perimeter of the Sudoku grid but the implication of that is that this cell turns gray and has to have the same number in it as this too and that's not going to work because this is a Sudoku grid and every number in its column has to be different so that cannot be true and we know that we can't you know we can't have the Sudoku grid ever overlapping the edge so the only way this works I'm going to contend the only way this works is if this is gray and therefore these cells well actually hang on this is taking this too to the seven by seven I know it can't run here that does or actually hang on oh now I'm now confusing myself again am I saying that this is the edge of the Sunoco crit now or am I saying that if that's the edge I know that this is a cave clue I do know this is a cave clue so it must see a gray cell so if that was in the 7x7 it wouldn't be in the cave and that would break it because it would force this to be the cave cell and that to be at the Sudoku grid which it can't be right so this cell touches seven by seven which means that this Somehow Here is the left hand side of the Sudoku grid now how do I make use of that I do not know well okay I know how you make use of that this I've decided is part of my seven by seven so so it must go that way seven one two three four five six seven that is forced this is sudoku grid and therefore this is sudoku grid so maybe I go to the pen tool let's do actually I don't like that green color I'm gonna go black there we go like that so we're going to have an interior of bluenesses which is going to be seven by seven in the end and then so we're going to have sort of a I don't know whether to do it an internal color here or not I'm I'm confusing myself a bit um but anyway the the dark lines we have to just remember are the Sudoku grid they are delineating it's a 9x9 and that should be nine cells now so that cell is a two because that is a gray cell it's part of the perimeter of the Sudoku grid this is good right that's what this two is doing isn't it that cell now cannot be part of the Sudoku grid because that would put two twos in this column so the furthest up that this can go is here one two three four five six seven eight nine so it has to go down here which means all of these cells turn blue that's lovely this is all Sudoku grid down here so this is all Sudoku grid down here okay so now now what I should be doing I guess is to we know that this sells part of the we know all those cells are part of the cave so we must isolate our island with a bunch of greens so that that's all forced don't oh I was about to say don't make a checkerboard is that is that now legitimate given I've got my one checkerboard well actually you can clearly see this can't be gray because it's going to box in a box in a green so that must be green ah now what about that one then is that green if that was Gray yeah it's it's it's it's fine that that is not gray because because I think the earlier logic I've got to trust it basically I have now got this wall this is effectively an orthogonal blocking wall so this checkerboard provided me with an orthogonal blocking wall which prevents me um from connecting these two up in any way that's going to be helpful because remember this has to get either to the edge of the Grid or to the edge of the Sudoku grid now if it gets the edge of the Sudoku grid this green is isolated if it gets to the edge of the grid this screen is isolated and it must do one of those things yeah and previously there would have been the opportunity for it to slink around the Sudoku grid like this and meet its friend like that but the orthogonal wall prevents that so that cell is definitely green and we can now up so that means these two by the same token any any other checkerboard in the in the grid is now is now fair game for us doing some Logic on it now so how how big is my Sudoku grid so far I've got four definite ah now does that mean that no uh I was going to say does the fact I've shaded this mean that this has to be part of the Sudoku grid but I don't think it does um what we want is I'm looking like sort of trying to imagine I've got a Sudoku Grid in this part of the world I'm trying to see whether I can get the same numbers into rows or columns so that I can immediately say well that's impossible you know a bit like we did with the twos here um that definitely is in the Sudoku grid so that that digit is at least a three because it sees three greens that's the world's worst deduction isn't it that is the world's worst deduction okay um yeah oh okay I don't know whether this is true or not I'm thinking questions like how does this two ever connect to the edge of the grid I don't maybe that okay so maybe you can ask general questions like can this ever be Gray because I don't know that it can be if I stretch the Sudoku grid as far up as I know it can no I'm talking absolute nonsense oh but hang on orthogonally connected to the 7x7 is not going to work yeah for this to connect to the middle bit of the grid it has to hit the seven by seven which is actually coming up this way and it definitely can't touch that in two cells so that and it can't get to the edge of the actual Grid in two cells so I'm going to claim that sells green now that means it's got we can't do a great deal with that can we now what about these ones then do I know what these what their nature is maybe it's easier to think about once ones oh ones could be in the seven by ah oh my goodness this is it I've done it I've done it wow oh that's so clever Magnus it's so so clever is so clever he's making me look so stupid here now right how can a one exist in the middle of this puzzle we know that if there's a one in the middle of the puzzle there are only two ways to deal with that the one can never be a green cave clue so it could be a gray cave clue that's very very true but if it's a gray cave clue it must connect to the edge of the Grid or it might well the edge of the Grid it's in the middle so how does you connect that if that's a if that is a k valid cave clue got to connect to the 7x7 and I can see only one way it could do that now if it's neither of those things that's fine if it's in the 7x7 go back to the example again look there are loads of white ones in this grid but they are in the 7x7 everything that's not in the 7x7 has to be Gray so how does this exist I can't now I've got this blue this is the development of my seven by seven I cannot get these two ones into it it's impossible won't go high enough that's the as high as the 7x7 goes so these two both are valid cave Clues they're both therefore shaded and far more interestingly or not as well just the interest just keeps going now yes I'm not a guy you want to talk to at parties unless you find this sort of thing fascinating but how do you connect this to the edge of the grid well it's got to be connected to the 7x7 so that's the seven by seven fixed that's forced and now we know the Sudoku grid so that so we can just ring it this is the Sudoku grid which must ring the 7x7 oh that's lovely uh let me just check I've got the right size I think it is the right size it ought to be ah I feel I feel pleased about that now well now I know what I'm going to do next thing I'm going to do is I'm going to divide up the Sudoku into lines so we could do this can we wait let's do that so that we can actually see whoa we can actually see if there's any Sudoku we can do yeah there's little things we can start to do now there's a one in one of those two cells um there might be more things we can do but the next thing that's tempting me is that these ones obviously are real cave Clues so they have to be bordered by greenlinesses uh and oh and I'm going to be able to do my checkerboards now because I can't have any more checkerboards so that's got to not be uh Brown uh gray or that would create a checkerboard these two have got to be greened um I have no idea what that means uh well hang on that that too now can't come here can it if that were and what I mean is if this is green two is broken so that's great and this gray has to either get to the edge of the seven by seven or the edge of the grid um ah okay what about that cell now that's catching my attention that is a green digit so it so what I'm going to fill into this cell is how many green cells it sees north south east west well it only sees three cells I think that's a three and I think that's a four by exactly that logic this is starting to fill in my Sudoku oh this is so cool isn't it oh now this cell has to be more than one two three or four by Sudoku so it's at least five and it's green so it's got so that's turning both of those cells green there's at least a five um so five six oh well is that you worth doing is it worth actually labeling those green cells up five six sevens eights and nines I think it might be I wouldn't normally do it but I think in this puzzle where I need to count like that can't be nine right okay that's the next thing I'm seeing is that there's a relationship between these three digits they are a sort of Ren band sequence I'm going to claim by which I mean well this cell if we look at what it sees from a cave perspective let's go it sees those cells and it sees everything vertically that's green this cell sees the same vertical sequence that this one sees so it must see a different number in its horizontal sequence otherwise it would contain the same digit as the what cell above it and that has exactly the same property so what this is saying is that for these two cells we're going to have to have this got to be Gray to the at least one gray to the left of both of these and one of them has two grays um and I've got to do that with or is that true or maybe I no I think it maybe it is true that one of them's got two Grays because if they don't I might not checkerboarding again so I was thinking maybe I could do it like with a gray here and a gray here instead but that would put greens here and here and that will create a checkable which I know I can't have because I've already got my checkerboard up here right so I'm now going to claim I think this is right but I'm not I'm not a million percent certain um I think that those three cells contain exactly three Grays I think but I'm not sure that's actually helpful because I don't think I know where they go so if that was nine these would be an eight seven pair uh okay this this digit has to be capable of being too higher than whatever I put in these so the minimum I could put into those two squares would be a five six pair so this must be at least equal to seven because it's counting these two cells so one of these is just counting the vertical strip ah yeah okay so one of these because this is at least seven or the other way of seeing this is that this this vertical strip has to be at least five doesn't it a five continuous greens so we've got to get here and just to reinforce that imagine I'd had made that five which was previously an option what on Earth would I've put in here well this would in order for this not to be five there would have had to be a gray in one of these two cells and that would have made it less than five which would have been an illegal digit so that that I think is sensible Sound Logic that can't be nine for the same reason then but one of these could be eight if this is nine uh let's get rid of my red line here I think that's probably otos now so this is a strip of at least five vertically and this cell is therefore five six seven eight or nine by Sudoku and that oh I see right and that's going to be able to see along the Sudoku grid in order to correct its count away from whatever these three digits are oh so does that mean that has to be green I think it does imagine this was not green now this cell it's seeing the same string vertically as these three cells and it can't see a different number horizontally because whether I gray these or not every single combination is catered For by these three digits yeah so that's got to be green foreign I don't think that's really doing that much you know how long have I had nearly an hour nearly an hour and I well I have got digits and I've located the puzzle so that's maybe not the worst thing that's ever happened in the history of Sudoku um but I'm very much unsure about how to how to do do whatever I've got to do next um can I think of anything clever here seven six five these would be an eight nine pair this would be gray if that's seven that would be Gray there's nothing wrong with that that I can immediately see if that's eight these would be a six set so it's either seven six five eight seven six or nine eight seven so there's always a seven in this string of digits which means that's not seven and that's not seven which ah hang on that can't be nine can it because it's got a Grace ah yeah hang on this the count of this sounds interesting oh this is where we should be looking okay look at this cell that's at least a five and it's it's in a little Alleyway so it's only counting these cells so one two three four five six seven it's maximum size is seven so it can't be eight or nine so that is five or six now is I want to if it's six it's really useful isn't it because if it's six I think the only way it reaches a count of six if if it's exactly those six so if it's six this would have to be nine eight seven and that would have to be five but that oh no this doesn't work there's something wrong here yeah okay that can't be five I'm now realizing because because it because it needs to see a different total from the hot from the vertical string otherwise it's going to match off with one of these two and it already sees five so so that's why we had to put this green in was to stop this having the same count so that is at least six so now if that's six because this is a rem band string it has to be 987 that has no actual option so this is five and that's it's good but it's not the digit we were hoping for so now the problem with this being far well I suppose what I can do is those two must both be green because even if I take that digit as green it was still a string would still get me these two as green all right um so this oh oh no no this is better it's actually a lot better I don't know why I can't see these things oh dear dear dear right this being five meant that even if I took this I have to take these two but now I can't take this one because if I did it's becoming six so this is actually useful that oh good grief right hang on this cell is not a one or a two that's at least a three so we've got that's got to grow oh that could be exciting he says realizing that actually it's just stopped there but that was that was quite exciting for a moment so that cell is now green um now this string of digits 987 876. and we can't have 765 here this can't be 7 anymore because these two can't be six and five right so that is not seven this is now eight or nine so if is does that mean this can't be eight it can't be eight now can it because this is either nine eight seven or eight seven six so this cell is now either six or nine and if it's if it is six it's already seeing all of its six so that cell that cell and that cell would all turn gray um I'm sure that there must be a reason that that doesn't work but I don't know what it is uh any ideas anybody I just needed to I just needed to see one more cell and then I could write nine in here oh I think I can do that actually hang on what how does this achieve a count of eight now because this had to be the five this this which sees two here must see at least six vertically so I can do that and once it says this sees six vertically and sees one horizontally it can't be six anymore so that is nine wow so that's eight uh this is now a six seven pair this okay so this eight is seeing I think it's seen it's it's quota now so that self has become Gray might connect to the five which would be useful so the nine is seeing it's seeing six vertically seven so it needs two Mark could be just those two so I can't extend that over here I don't know what this this how this nine develops its count yet and the six seven here well we know that that's gonna be either like that or like that or something like something like that one of those two things I think right so nine is now over here maybe it's Sudoku we've got to do or maybe not um let me think that's if that's a one what's that saying that's a valid cave clue so it should be ringed by you pentomino like this one and that's not going to be what right because the 2 then is going to become a three it's going to see three cells so that is not a one this is a one that's the world's most disappointing one isn't it it doesn't do anything that's probably a two is it to connect with this I don't know um foreign the other things that would be useful actually thinking about it these two digits aren't they if I knew oh well yeah hang on hang on I've got something here right these two digits C5 horizontally so they are at least equal to five they must in fact be greater than five because otherwise they will be five and they will repeat in the row of the Sudoku so these are bigger these are sixes sevens eights and nine so they both must see green cells above them oh this is beautiful good grief okay and because these both extend now this cell if that was gray I'd have a checkerboard and we can't have another checkerboard so that's got to be green completing my two clue so my two clue gets ringed on eel all of its potential sides by graynesses avoid a checkerboard grayness avoid a checkerboard grayness this clue is now known that C6 oh this is just so clever wow just wow this cell can't be gray now because it would be in a part of the sixth Island and it was count would be five so that's got to be green which must C5 so it's got to see those cells can't see this one or it would see six out this is just brilliant this is quite brilliant so this now does C5 that one well that one could be part of the gray cell maker T in the grid or if that's green it's got to be it would have to then be the a string going to here and then that would be great let me look at that for a second that would be Gray that looks quite good at oh hang on that's got to get to the edge no that's hang on this has got to get to the edge of the grid ah okay this doesn't work I'm just trying to see if there's an easier way of seeing this which there may be well I I don't think well let me just explain it if this six is green this gray has not got to the edge of the grid now it can achieve an edge of the grid by coming along here I'm meeting up with these friends here but you can see that to do that it's still got to get to the edge of the grid so it would have to connect here it couldn't connect here because I think unless I'm wrong that's creating a complete wall there and if we know we can't have a complete wall here because this checkerboard needs to find a way of of getting its green to circle the Sudoku grid so that won't work and the same is true here if if we do something like that well the reason that doesn't work actually might be different the reason that doesn't work is that this string of Grays now is bigger than 9 to put in that cell yeah hang on let me just unwind this a minute so maybe the way to think about this that's simpler is to consider this cell now we can't have another checkerboard so that cell's got to be Gray and now maybe it's easier to see that if this green comes over here like that and then ends you've got to get this gray to touch something the only thing it will touch is this and I think that that is more than nine it's it's 11 I think and I can't write 11 into a Sudoku cell so it doesn't work wow that's complicated actually though that is complicated but it's it's brilliant because it means this is gray and if that's gray it's completed its shape size so it must be orthogonally bounded by greenliness we mustn't make a checkerboard so that becomes green uh this is a nine it sees nine sees five horizontally and four vertically so we can just write nine in there which means there's a 9 in one of these three cells by Sudoku that cell is now at least a four well that's actually interesting it's at least a four it can't be five six so it's four seven or eight into this cell I would love it to not before although maybe it would be better if it was four all of those would become green this cell is at least oh this cell is at least a three because it can't be one or two by Sudoku and it's only seeing two at the moment so that cell turns green you see if this was if this is a big number what you can't do is create a wall of Grays I can't connect this shape to the the top edge of the grid because that's going to prevent this cell and this cell connecting around the edge of the Sudoku which we know has to be achieved so actually maybe maybe the solution here oh no hang on what I want to do is to put the options in for these remaining digits in this row I wouldn't normally do this you know I wouldn't but this is quite complicated so I feel I feel Justified look those can't be sevens by Sudoku this this can't be a two by Sudoku so two is in one of these cells 2 is in one of those cells I've got to ignore all of these twos in the grid seven is in one of those cells I've just seen so seven is in one of these two cells right can that come Ah that's beautiful that's beautiful right so now how could that be a green seven it can't see seven vertically so it can't be a green seven aha in fact I've just seen it also can't be a green eight so that is a green three or four but that is a seven that mustn't touch the top of the grid so that cells must be Gray uh one two now this cannot be gray yeah so one way of thinking about this is that to connect this green region we've got at the top of the grid to the rest of the green like down here we're gonna have to come through this little Strait of Gibraltar here we're going to have to come through there now this is five so it's got to grow at least one more here that green has got to grow again this this now is clamped out of three good grief so none of those are three I've got a two four eight triple here don't use the four that doesn't matter um wow okay come on what does this mean there's a four in one of these cells by Sudoku do I know what that is surely I do um I don't know actually it depends how this seven achieves its its quota oh no come on come on what do we do next one hour 13 minutes this is about this time when I start to worry that this is going to be an enormously long video but I also start to worry that the software is just going to glitch at this point and then I will just cry um wow where do we look though is there an obvious place do this can that be a you do I know somehow which of these is the two or indeed which of these is the eight probably do um I've still got to put ones in the perimeter ones that I love once in the perimeter of this Sudoku because they they actually give me Immediate greenage don't they but unfortunately don't think we know where these ones go oh hang on what's going on that cell can't be a two now or a one something going on with this cell this cell I think is is under pressure because what what color is this cell if that was Gray it would have to be at least a three and we know it would have to stick straight out because if it comes into either of those two cells it's saying those two cells would have the same number as itself in order to be in the same size Island so that doesn't work so this cell is undoubtedly green I hope that takes all the pressure off it that's weird that's so strange all right so let's fill in these digits as they're fill in the options for these digits three five six nine now this this is allowed to make this green I think if it sees a green either above or below it so now I can't say anything about this 2 which is infuriating no that's not true I can say something about this too how could this two be Gray that's really it's just it's again it's another simple deduction once I have the idea of thinking of this through if that's if that is gray it needs to touch the edge of the grid which is either the blue or this edge of the grid and it can touch neither so that cell is green which which means it's seen his quote that's ridiculous it's ridiculous that you can just get get that oh my goodness right so it sees two so that must be gray that must be gray that must be gray don't make checkerboards all of those are gray good grief this now is going to be struggling I think to be anything other than three although I can't prove that I mean okay I suppose maybe no maybe I'm wrong is this connecting to the 7x7 or is it connecting to the to the right hand side one it could do either it could do either still especially if that's a big green number and sort of striping a big green through the grid there uh okay right okay but now now these two cells can't be ones can they because we know wherever one appears in the perimeter of the Sudoku it's ringed by you pentomino of greenliness and you can't put you can't put ones in those two cells so that could be a one is this this is too effective ah ah okay in fact if you put one in the corner what happens you can't put one in the corner nobody puts one in the corner because if you put one in the corner it's still subject to the same difficulty it needs to be gray but it's never touching the seven by seven so one doesn't never go one's never in the corner one isn't in those cells so one's in one of these cells now I'm wondering whether we can do some magic here that can't be a one because it would be surrounded by a green new pentomino and the two would be green and C3 so that's not a one now is this is the same logic applied does this is beautiful you can place one in this column if that's a one it's surrounded by you pentomino that too is broken it sees three cells so that is not the one this is the one therefore it's gray therefore it's surrounded by greenlinesses so there is now a one in one of those three cells I don't know what's that I don't know what that's done but it felt it felt dramatic um that is now not green because if it was green it would see four so that's gray and needs to get to the seven by seven because it can't get to the perimeter of the actual grid so that's gray and therefore is it two which therefore must be bounded on all orthogonal sides by greenlinesses don't make checkerboards what about that then is that able to be green really maybe wow okay I'm not sure whether I can state with any certainty what that one is um okay but presumably now presumably there is an issue regarding the Sigh well that digit for example the maximum number of greens it could see is six so that is a number that is a maximum of six and is not one or two so that is three four five and six that cell can see greens above it so we don't know about that one three four five or six here two four eight up here okay sorry I'm not sure whether I can do better than that I probably can I mean can that really be nine it would see eight vertically eight greens vertically no that okay that that is actually impossible because this can't be an eight yeah that's complicated though so there is a relationship I think between these two digits if this is nine that it's going to turn this cell green and the count in this cell is going to be one different to the count and this cell because this cell C is one in its East-West Direction this will see zero in its East-West Direction so it would have to be one different now actually I'm not going to try that again uh six and five work though five and four don't work can that be five if it's five it does turn that green and that's going to break it again so it's not five if that's three it's there it's still great it's still great if this is three how does it get its third cell Well it can't get it here because that will make it four so it must get it here and turn this green in which case this is seeing one less than this so it should be a two and it can't be so that is a six which means that this cell well it still does turn that green because it does because it needs to get reach a count of six but we now know this is a five so this is now seeing five vertically so even if it takes that one it's definitely taking that one um and now we don't know it could take this one or this one in which if it goes upwards it takes two more but that's now become not able that's not a that's green and not able to be two in fact it's not able to be four because it's going to see it's going to see five vertically isn't it five greens vertically so that is now eight which means these are now a 2 4 pair do not use the forehead um okay so this is seeing eight vertically no not eight no because it can see horizontally it can see horizontally so don't get excited that's nonsense well this is seeing it's saying five vertically so it must be saying three horizontally so if that becomes green well no hang on if that if that's green whichever one of these is two is wrong because you're going to see three in that direction so that must be Gray and it must grow so that must be gray now do I now know which of these is two oh how does that no I'm going mad I think I don't know I still don't think I know that's so weird okay well I'm sure I do know and it's just my brain is letting me down but I'm coming back to this eight now because this is telling us we see five greens vertically so this needs to see three more horizontally so all of those must be green and in fact that must therefore end in a gray in order to make the count correct so that's quite a nice deduction and in order to no we still don't know five six seven eight now I still don't know about this cell right but now ah that cell has not is not five or six anymore this is three or four and in this column we've got threes fours sevens and nines to put into into the Sudoku positions now can we get rid of anything three comes out of that one um nothing comes out of this one nothing comes out of this one I don't believe it but that's green the maximum count this gets vertically is five isn't it six so it could be seven or nine if it starts to grow in this direction enough so if what about that cell that this cell depends on whether this hits the boundary or not doesn't it if that's gray is that really well yes I suppose it could be a seven or a nine that seems very unlikely to me that that's Gray I'm not sure I can rule it out it is two both of those oh that would be really powerful if that's two if it's four those two both turn green that then would be a two so these all of all of those would suddenly turn green that looks that almost looks likely to me and I say that because I think that gets the eight correct so here let's come back to that then if that's two and that's four let me look at that if that's two and that's four because this then has to be Gray that would have to be great to avoid a checkerboard this 4 is then done so all of those turn green and that one this four clue is green and seeing three that's green uh we got some sort of checkerboard thing going on here that's green to get that green out actually so that four is now completed turns the two gray which would have to hit the boundary it would go miles absolutely miles if that's true but I don't think I know which way around they go that would be really I think I think that's probably the next step but I can't see it immediately in terms of how to do it and that's infuriating so what could it what else could it be what else could it be this is green if that's a green three it would have to be this green and then that shaded that might be possible I don't know oh if that's three that's four that would make this green and this shaded I don't know I get again it doesn't seem it doesn't seem very easy to know which of these is correct what about oh hang on that sells gray that's got to be gray because if it was green it would see too many cells that's been available for ages so that must be Gray uh okay that's that's very very underwhelming that does nothing okay so for those of you who've been shouting at me about that I totally understand but I think we can now both agree that that was not the next step in the puzzle uh it's a step what about this five five combination down here can I if that's green then at least those have to turn green if it's if it's gray everything everything's easier do those fives have to be part of the same clue I don't know not sure okay let's try let's try let's try Sudoku which uh feels like a very difficult thing to focus on at this point but it could be relevant right so let's try this row look we've got to place four six seven and eight into these cells ah so that's a four six pair so maybe it is sudoku so that's a seven eight pair now if that's a full six pair we can say with some confidence that these cells are 5 8 and 9 and that's not nine so these cells have got to be two and three problem is the these blue ones don't do anything the only way they're going to be useful for the cave is to the extent that they affect the the very perimeter of the Sudoku puzzle an unfortunately I'm not saying how they do that oh that can't be nine look by Sudoku that's perhaps worth recognizing is it possible for this to be nine is that would be a green nine wouldn't it and it would have to therefore pick up this cell which would cap it out vertically at a five count so it would have to have four cells this way so all of those would turn green whereas if this is nine what are we then saying we're saying that that that would have to be a gray nine and connect to this which which wouldn't have reached a count of nine it would have only reached a count of six so it'd have three more cells to build on which could be those three uh if it couldn't get to the edge because that would create a wall of or a wall which would be a bad thing um right okay I don't know how I decide which of and I definitely know there's a nine in one of those two cells I definitely know there's a nine in one of these cells uh okey-dokey I don't know where to look I'm sorry if everybody knows do I I know this digit what do we know about this digit I know this nine is seeing s thing 5 in that in that little Alleyway that this one doesn't see so it's seeing it's seeing itself and three this way so this digit ah that digit's at least a five then because because it can't be four by Sudoku so that's got to be five or eight only which is perhaps interesting although I don't quite see it looks like it should do something doesn't it but I'm not sure it does we know that this green this green here is seeing four this way so it must see this cell is that the deduction we get from that yeah I think that's the deduction oh maybe it can't be eight ah yes it can't be eight that's it there you go this this cell of all the cells I should have been focusing on apparently it was row nine column two or in in in in the other way of thinking about it row 13 column two or column four because had I focused on row 13 column four I could have seen okay this nine is seeing four this way so this is seeing four this way it can't see at more than another three so it can't be eight so it must be five that cell therefore has to be gray don't make a checkerboard now this screen must be green because otherwise it's part of a four region so that's green um these cells are now sudokui they're sudokui aren't they ah I didn't mean to do that I want to put in one two three and eight in there yeah okay that's good that's a good believe it or not I think that's good because that two three and that one two three eight form a quadruple and make that a seven so that's an eight that's not eight anymore there's got to be a one and an eight so that's now down to two or three I've got a two three pair in this column and those squares have got to be one six seven triple and that's not six and that's not one and if this is a one six seven triple you've guessed that these are four five and nine which I can't do anything with infuriatingly that cell's not able to be a two because of this two foreign absolute rubbish um do I know the color of this cell I think that would be a useful thing to establish it would it would be very useful if it was Gray because if it was gray it's almost creating a wall that couldn't exist so that would have to be green so if that's gray it has to be a one if it's if it's green it would have to be an eight because it's seeing four this way and it can't be an a to gain because it was eight it can't it can only pick up three good grief right so right the point is this is huge again it's a beautiful piece of logic if this cell is green we know it's higher than a three in count so it has to be an 18 count when it's only receiving four horizontally and it can't get to eight vertically so it is actually a gray cell now what the problem with that is that obviously being a gray cell it can't take this cell because that would create a an orthogonally green blocking wall which would pen in the checkerboard that we found so it must be a one and therefore we get the ring of a sort of you pentomino ring around it we can delete some things from these cells by Sudoku that cell's not able to be a one anymore I've got all the ones now in the Sudoku perimeter which were the the most constrained digits so that's a shame that cell's not green anymore because the two would see too far so that's gray this it must see here which forces this to be Gray this green has to get out so that's got to be green that cell is now seeing at least four um so I'm definitely pencil marking this I'm just trying to see if it's easy to see what it's got to be okay so by Sudoku let's just do Sudoku on it it's got to be 3 4 or 8 I think it sees one two C's five six seven and it sees nine yeah so it sees six different digits so it's three four or eight but it's we know it's seeing four so now it's at least four or eight if it's four this cell becomes gray and would be at least a two or that would again be huge in fact that's an interesting point where is the two by Sudoku in this box you can actually see it's in one of those two cells so this big two so what there is a strut coming down for in one of these positions that's a a two Domino of grayness um and either way either way this cell is always green because we're going to have to get this green across to the right hand side of the grid so if that's a gray Domino you can see actually that would force this to be green as well in fact this is always green both of those cells have to be green that gray is already connected to the edge of the grid so it doesn't have to achieve any greater size um oh look this is going to be a gray five isn't it if it's a gray five that's green I would have to get out so that would be green that would be saying that this needs to C5 so it would have that would have to be green as well I don't know uh right so if this is eight the world is oh now I'm suddenly worried I've made a mistake here I said that one of these had to be two and former gray Domino coming down but what's wrong actually with whichever one of these is two being a green two ah yeah that could be true I'm not sure there's anything wrong with that I mean it's true to say one of these is a two by Sudoku but I hadn't thought of the fact that they have to they could be agreeing to that's really annoying this is an eight a lot of this row is becoming we got four here five six oh that's right that's it it's just simpler than I've been making it if that's an eight those four have to turn green and that's going to make this eight into about an 11 which is not going to work so that is a four and that's great because that now has to be Gray which probably means it is the two but I'm not certain about that now I'm slightly worried about my two logic um we know that this must be green don't we because these can't be part of the same island by Sudoku because they must contain different digits so that's green it can't be a one so it has to get out now this is that both of those are now green to get this green to pass through from left to right so the question now is can that be can that really be gray I'd love it to be gray it'd be useful because then this green would start being under pressure four comes out of this corner cell so we're down to three or seven in this position probably I have to pencil mark this cell I think it's either two six seven or eight by Sudoku I mean I'm almost certain it's going to be two but two is two it would have to go there a bit because it couldn't come down that was two this all on the other hand if this was not two that might be how the puzzle gets finished because we still see it still feels to me like we're you know we've got a lot of extra thinking to do to understand how on Earth all of this gets resolved um you can see that making that sort of six seven or eight and having to build it out over here is going to do all sorts of work I think I've got a pencil mark this cell as well though right so in theory that cell has the ability to be two three six seven or eight all of those are possible although I mean some of those are going to be very very difficult is it possible that all of those are green gosh it's only just possible for this to be a green three now it would have to be ringed on in all those positions by Grays that would be really useful to know really useful to know wouldn't it foreign I wish I could I wish I could understand how whether or not that's possible on the other hand if that's three then that would be four and everything would start to get resolved complicated that's what this is one hour 40 was another he knows might even be longer than the video I had to do on the rosette puzzle by gliporal it's funny uh and don't get me wrong this is a very hard puzzle for me at least I'm finding this very difficult and very interesting but it didn't feel I feel like if I sit here long enough I will I will solve it in the end whereas with the gliporal one I didn't have that feeling um it's funny how puzzles affect you mentally now what I've got a feeling this could could even be Sudoku that I need to think about to solve this one of those three squares is a four by Sudoku one of these is a two I mean it's so beautifully minimal as well isn't it it really is I mean this very little extraneous information has been given to us I'm trying to see see if there's some sort of chronic meta connectivity point that will allow me to figure stuff out a bit a bit more quickly but I can't see anything it's here um two three six seven eight into these squares so that square is two three six or eight uh that's not two actually hang on that's not two is it so that's only three six or eight that is a three that suddenly becomes a gray six foreign well I'd have to be careful that that gray six didn't hit the perimeter down here so it would be really powerful again I think everything that suggests this is a well three in the corner no doubt that man no down Magnus made this a three in the corner it would be a very useful digit indeed but having said all the Hat unfortunately ah I don't know how to do it um is there a way for me to tell whether this I can't remember what how many is this seeing this is seeing five vertically isn't it is there a way to know whether this if that becomes green then this gray connects to the wall and that I don't think that's a problem I mean it might be for reasons that I can't fathom but I can't see why that's a problem because the green is still able to pass through that passageway and get down to the bottom of the grid or is it this six that's six if it's well whether it's gray or green it's quite interesting great it's got to get to the edge of the grid and it couldn't join this so it would have to might have to miss the five I'm not sure well it would have to miss the five but um I'm not sure whether that's problematic or not we could what else could it be is there a way oh hang on I've got a one here now blocking in my nine ah so I can now come back over here at long last and greenify both of those digits is that I'm not sure that's going to do anything I really am not oh that's so depressing has that affected these fives I'm not sure it does it's useful and I know that I can't have a checkerboard over here can I so I've got something like this or like this how are these fives ever going to get resolved I see I think I know how this is going to resolve I think somehow someway we'll get the six and seven resolved that will position the Grays around here and that will somehow limit these fives down here that's what I feel is going to happen okay let's try maybe it's possible to prove this can't be a big digit if that's a big digit you can now see we have we'd have to do that at least I mean it might have to grow more than that so this cell now we've got to get this green out so all of these would become green now is that for some reason problematic yeah Ah that's it that's it yeah it's not too difficult once you see it right it's not I'm not saying it's easy by any manner no means but let's come back here remember if we get a string of greens they can't have the same count so by making this six seven or eight because both of those turn gray and this green has to get out these two greens here will have the same count they're only counting horizontal digits so they would contain the same number so that is that's lovely I mean to be honest it's lovely like I've got nothing but respect for that as a deduction it was totally and utterly fair I just had to have the right thought um so therefore this becomes the gray digit that therefore oh bobbins bobbins it can still be three so that's all pressure all pressure comes off this digit does it and that's got to be three six seven or eight and it can be any of them oh dear oh dear that's really depressing that you can get this digit and it does nothing there's now a two in one of those two cells by Sudoku if this video by the way triggers over two hours I'm actually gonna stop the video and then restart it so I so I don't lose lose all this work it's very very rare that that we asked movavi to work uh for this length of time and it is not the most stable piece of software in the world so um I carry on for a bit but if we get to that point I'm going I'm not I'm not risking this solve being deleted um three six seven eight so if this is if that's eight for example all of this turns green doesn't it one two three four five in fact if it was eight exactly that string of digits would be green none of them could be three oh hang on that's quite an interesting thought I need I do need to put a three in one of those cells and obviously if all if these two are both green it's seeing far too many cells in that direction so that cannot be eight now can it be seven one four no it would again it would make these two both green I'm not sure it can be six this would be so cool if this can't be six if it's six again how do I do it there's no way to make this a green six without taking those two cells thereby making it impossible to put a three in that sequence wow so that is three which makes that a seven in the core it's a seven in the corner no oh whoa but I get a gray digit here and a gray digit here to cap out my three this this looks like an interesting number because that's got to stick out because it can't take that cell which must now be green because otherwise these would have the same total so this green has to come down here look that's got to bend oh this is this is free and dandy it's fine isn't it right if that was eight it would be saying there's eight horizontally which there clearly can't be so that's six that's eight so that's a big number coming in here this seven now is seeing one different it's seeing six horizontally from this clue and it needs to see one vertically so that becomes green pushing my eight down might have broken the puzzle oh my goodness have I broken this because this has got this has got to grow well it's got it cannot come to the bottom row because it's going to cut the greens that are around this checkerboard off so it's got to stay away I think it maybe it can do that this suggests this is correct as well doesn't it look look look look like that becomes green don't make a checkerboard if that becomes green wow wow this is great now I can fill in the greenliness of this six sequence one two three four five that's green that's got to be gray that completes my three clue so that must be isolated on all sides orthogonally don't make a checkerboard wow wow this is so exciting now I know I'm a strange man and I find strange things exciting but this is very exciting for me um right so this is now four or nine it can be it can't be ah it can't be forever whatever color it is it breaks if that's a four and we make it green it's seeing five vertically if we make it four and we make it gray it's seeing too many that way so that's a nine whoa that was not what I was expecting so it's a nine do we know whether or what color it is now yeah we do actually because if it's nine and it's green we know that because of this five it's only seeing five vertically so it's gray ah so it's part of this that's a green three or four so that must be green oh this six looks very very difficult doesn't it oh it could be green if it's green and that's gray it works it probably is then okay right this is exciting though right have I now have I now done something clever Sudoku wise that's now not nine I felt like I got loads of digits down here has it actually done anything ah yeah okay this five clue now needs to see two more vertically and then make that cell Gray so this eight clue now is correct this is it looks like it's doing some work with the two and the four up there doesn't it so that's potentially exciting well yeah okay okay how is this now a grave for that would push this up to be Gray now we can't now take this or this is going to be a five cell gray sequence and in doing making this green we create a checkerboard and we know we cannot have another of those so that's lovely that is lovely so this is the two this is the four now I thought when I looked at this before I thought any arrangement of this was massive that's got to avoid a checkerboard this four needs to C4 so that becomes green that becomes gray avoid a checkerboard that becomes green that will be isolated if it was gray so that's got to be green this for probably it's I can see if it's green it's got the correct count assuming that's gray if it's gray that oh it's weird it works both ways how strange is that I don't think it can but that looks wrong because this green looks very difficult to me um but let me just smold this over for a moment or two if you don't mind gosh it might it would be so easy to make a mistake here as well with it that's gray by this being a seven count now okay let's think about this then so if this is gray you can see that's gray to avoid a checkerboard which means all those cells have to be green which breaks the two because by checkerboard logic this cell would also be green all of those would turn green the green would see the two would see three so that's great so this is a green four which means that's a gray to make sure it only sees four cells that's a gray this now can't be gray or it's seeing too many so that's got to be green which I wasn't expecting actually avoid a checkerboard so that's the two greens we're allowed to see so all of those become gray don't make a checkerboard whoa whoa okay that oh that gray has not seen an edge so that's got to be Gray oh look it can it can't close here I was thinking that couldn't be great because it would cut the greens off but the greens rather naughtily have sneaked down sneaked down there they could go like that okay bobbins right all right so do we know what's going on in the corner now if there is a three in the corner it doesn't get a song If that is a what's going to make it difficult for this too if if that is if that's if that's gray what happens to the world well if it's gray I can see it can't be a string like that because then all those have to be green and the two would be broken and that would be the same if we put the three across the top there so the only way that this is a gray 3 is if it's exactly like that and that would be green and that would be green and that would be green and that would be green and don't make a checkerboard and the two would see too many again right that's lovely so the three in the corner is green now does that mean this is cray or does it mean it's green and the answer is I don't know I mean it can't be green if the three does that that cannot be green it would have to be Gray if the three does that it's complicated isn't it it's complicated if it does that what color is this wow okay if it does this this is still not green because if it's green let's think about how this would now work for this three clue that cell has got to be this two has seen all its digits now it's seen those two cells so all of those have to turn gray but from the three Clues perspective that's gray as well so the three would be either these this green gets isolated wow wow so that right so actually what we can say is we don't know what this three looks like but we do know that this is gray and if it's gray it's not coming sideways now because that would break because it would join to a huge region and not be a size two but I still don't know what it does I mean the green could come that way and then that would be gray and those three would be green or or the green can the green do a little thing like that no no that's going to get isolated if it tries to do that so it's it's definitely a stripe it's a stripe there or a stripe there if it's a stripe here that becomes gray that becomes Gray that becomes green oh I've got a horrible feeling we might have to sort of do this both ways around and there might be some cells in this little three by three that are always one color um maybe that's what I do need to do is that gonna is knowing anything about this three by three going to impact the rest of the grid though I think I might be focusing on the wrong thing I I mean in in the sense that I can't actually see how this three by three is going to propagate down the grid so perhaps I don't do this next what about okay what about this three four pair here one of those is going to lead to a gray in one of these positions the other is going to lead to a green and then a gray so there's just sort of a gray X-Wing going on here either in those cells or in those cells is either of those problematic to avoid a checker if that's gray to avoid a checkerboard I'd make that gray that would give me I would give me eight cells of my nine cell region there so that would then have to be green that would make that gray that would Ah that's interesting so if that's Gray I know exactly what my nine cell region looks like and that actually looks very persuasive doesn't it I suspect that is correct oh no hang on that no that's wrong I'm wrong no sorry I'm now now gonna count them on myself and say I think that's now impossible because I'm suddenly realizing that I'm going to have a gray here as well I don't know and that's going to create a checkerboard if it's not connected to this gray so I think this doesn't work right let's do this slowly so my contention is that if this is 3 and this is 4 there is a problem in the world because this cell becomes gray and now this cell becomes Gray now we can't have a checkerboard so that's Gray now what is this six now well this six clearly can't be gray because it's going to poke out immediately and touch this nine clue so that becomes green which makes this gray and this green and all of these green and that's a checkerboard it doesn't work so that is the wrong way round so this cell is therefore well so we need to do it the other way around so that's four that's three that's gray that's green that's Gray oh bobbins bobbin's face is that do is that well I can see it's doing some stuff over here because Sudoku wise but actually I still can't even conclude whether that connects to that I think it's put less pressure on this six than was there before although it might be tricky for the six to make that five clue work gosh that would be a difficult deduction as well that could be true but I but while I've seen it I'm going to take the low hanging fruit of the Sudoku class two oh three eight so that's two that's three that's three and that's eight because of this three here uh that's really not done very much has it oh you rotten rotten rotten thing my goodness me okay so instead of that then we're going to come back over here I have Crypt over two hours but I don't want to stop it I'm going to risk it I think I feel like I'm not that far away now um now if this is gray my contention is that there is a problem let me explain this now got to reach a size of six without making checkerboards and things so this we can't make a checkerboard so this five sequence is forced but this hasn't touched the edge yet so it would have to touch the edge here this would have to be green and it couldn't be a count of five so that's great because it means that this is green and if it is green that's becomes gray and we must make a checkerboard to that because okay so this is probably well this is the same problem this has got to touch the edge and not break this clue so you can see if it touches well the thing is I suppose it could go up there and touch the edge oh maybe it can okay maybe that I mean it feels very much like this is going to be a gray five but I'm not sure it's forced how weird is that it is weird but what I yeah just to be clear what I'm worried about oh actually this is good let's try the nine go back to the nine clear I've got six cells in it that can't be gray because it would connect this to this to avoid a checkerboard and it would be bigger than nine so that's got to be green and now my nine is coming up into one of those two and then one of the or both of these two potentially so it's definitely coming into this column I'm wondering if it has to hit this now yeah I mean it's so difficult for me to believe this isn't gray but I can't if this was Green it would have to go push greens at least here yeah it doesn't work it doesn't work but it's quite difficult to see why not if this is green you can see both of those must be green as a result of that and this needs to oh no maybe it could get to the edge there oh oh okay there's no necessity for gray Clues to have digits in them is there I don't think I read that in the instructions okay well I can't prove that then I can't prove that this nine though it's got three more cells to take and we know that in taking those three cells it is not allowed to get to the perimeter of the Grid or it's creating a wall of graynesses which is bad therefore it's got to take exactly three of those No actually that's not true because it could take this one so if it took these two how does it not take this I suppose the question I'm now grappling with how does it not take that cell well it could take those two but then its next digit is impossible let's let's have a look at that so it's managed to not take this so far but we know it can't take those we can't take this because it would create a wall it can't take that it would create a too big a region um it now can't take this because obviously then it has taken that it was saying we're trying to prove that it can't take this and it could take this you might say but the problem with that is that that creates a that creates a checkerboard because this would then have to be green for the purposes of keeping it apart from this but that creates a checkable there so there is no way so that cell is part of this nine and the only way it can be is like that good grief that's really tricky so all of those get greenified don't make some any checkerboards over here this gray hasn't got to the edge so that becomes gray has this done this three clue the three clue couldn't be that could it the three clue couldn't be that I think I'd convince myself of that fact because yeah it gets penned in by gray so it can't take those three so yeah we said it was a stripe so it's a stripe horizontally which means that's gray completing the two clue which means that's green don't make a checkerboard that's green don't make anything bigger than two that's green there we go the top bit of the grid is done now if this is five if this is five you have to do this in the right order don't you it's really cool if this is five how does this ever get to the edge of the grid this five couldn't join up here or it would be more than five so the only way it can be five is like that and you can't now connect that to the edge so that is gray at long last we've proved it orthogonal connections to this island therefore are all green get that green out don't cut off the grid wow that's going to be that's right it's gonna be green otherwise the the green at the top doesn't connect to the green at the bottom so we're almost at the point of doing Sudoku wow in fact that's a bit frightening that's a bit frightening because I'm suddenly realizing apart from this I've basically done the perimeter of the grid which suggests there must be Sudoku Agogo that we can do at this point which surprises me mightily there's got to be an eight in one of these um foreign okay that might be it then because I can see that's going to push that to be a four that to be a one that to be a nine that to be a five by pencil marking which could do something for us so that becomes a nine that becomes a three these become two five and no two six and seven these become three five and eight that's not six that's not three that's not no it has not eight I'm sure there's a lot going on here that I'm just not appreciating but never mind let's let's keep going um where does one go in row seven this one up here means this is a one so there's a one in one of two places here this digit here is a six or a seven and confidently I don't know if we know the order I need to get this six and seven resolved that's that was my instinct three five eight nine in this column so let's put in some pencil marks three five eight nine now my phone is buzzing at me um take that at the moment three nine ah five eight pair is that gonna be it that gets me this four um what about that cell that's not eight that's not able to be nine or three I've got a 5 8 pair so that's nine that's three that's five that's eight that's three that's five that's nine oh go on come on be kind be kind that's five by Sudoku that's eight one two three five six seven now no five six seven here um that's not nine so fives and eights seem to be giving a little bit of Joy don't they um one two six and seven into these squares one two six seven that's not two that's not one what about this row two four six and seven two four six seven so that's not two I'm trying to spot things and failing really badly failing nah that too is useful isn't it that double two in fact is looking at that cell so that gives me a 2 6 pair and it gives me a one here which means this is a one by the power of pencil marking so perhaps these two digits which have to be an eight and a nine so this given nine so it gives us another digit nine and eight go in eight and five going um don't get distracted by the phone come on Simon come on um okay have we have we managed or maybe I do have to do this in order to influence the Sudoku to finish it that is also definitely a possibility um it's just not the one I thought was going to happen four six seven it does seem to all be about sixes and sevens though oh no two six two six seven there's definitely a four in here is there anything else that influences this middle grid I can't ah I don't know okay so is this really resolved then let's have a think okay so let's have a think what could it be maybe maybe it's as simple as saying is that gray if this is gray obviously both of those have to be green as does this by the oh that doesn't work how is this okay so this is going to resolve the six seven and it was a simple question it was just not one I was prepared to ask before but if this is a five because I have to Circle this in Greens and get this green out this five sees four and I can't make this green or it'll see six so that doesn't work believe it or not that is green and this now has to see quite a lot vertically it's got to see at least these but we don't know whether it sees this one or not it sort of depends doesn't it that now has to be green there's not enough space for it to be anything else so that's got to be green it sees three right if it sees the corner there's a problem because then it again it will see the wrong count this is being constructed by a total genius hasn't it so those two become gray this is now not seeing five so that becomes thing that becomes gray and now we must avoid our final job is to avoid a checkerboard here so that's got to be gray and that's I think the cave done and then we can get the count here look that is now seeing six vertically so that's six that's seven that's seven as a result of all of that shenanigans um which makes this six this five and that six is getting a six and a four at the top and a seven here and therefore that's a two that's a six that should be a four that should be a two that's a six and that's a seven I have no idea what's going to happen when I click tick he doesn't like it but I'm not surprised goodness only knows how confusing this is for the software but what a magnificent puzzle and I think I've solved it I'm really relieved two hours one of the longest probably the longest Sudoku video ever I mean it's a five star puzzle and I'm getting my head around the rules took about half an hour so I hope you'll forgive me I hope you enjoyed it I mean we don't do this that often but we do hear that many of you enjoy it for anyone who is still with me now thank you so much for spending this along with me on a Monday evening I really do appreciate it I hope you enjoyed it let me know in the comments I do enjoy the comments especially when they're kind and please pay tribute to this fantastic Constructor for what he has done here because imagine I mean it's hard enough to solve it as you've just seen for me at least but imagine trying to make it so that all these little deductions work so smoothly and beautifully and you get all of these little epiphanies as a solver it is mind-bending the cleverness of some people and I loved the puzzle and I hope you did too let me know in the comments as I say and we'll be back later with another edition of cracking the cryptic thank you

Channel: Cracking The Cryptic

Views: 77,904

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Id: 7RVIT4v5PCc

Length: 137min 0sec (8220 seconds)

Published: Mon Dec 12 2022