The Basic Tips For Hard Sudokus

[Music] hello walkabout of cracking the cryptic where I am gonna do a very quick video I hope today to accompany marks video earlier so mark did a review of Alex bellos new book which I appreciate didn't really have the normal puzzle content that we like to include a lot of you rely on us for your brain training every day so I thought we'd take a look at this puzzle which is coming from somebody I know in New Zealand he's normally a good source of or a good judge of a puzzle and said that they thought this was a very nice puzzle and it would make a good video sort of not a monstrously hard puzzle but just an elegant puzzle so we're going to have a look at that now if you wanna have a go first just click on the link under the video and that should take you to our webpage where you can have a go now the other thing to mention don't know if you've noticed it already I hope there is sound with this video but I am using a new microphone today now I hope it's an improvement and we've had too much of it too much bad feedback recently but some of you do say that the microphone is a bit echoey so I'm hoping it's better do let me know in the comments and yeah we'll take those on board as usual I'm just going to start you can see all I'm doing is fluttering around the grid trying to lock numbers into two positions exactly within 3 by 3 blocks so nothing more complicated in sort of spotting these two sixes therefore there must be a six in one of those two squares in this block and highlighting in the corners 9 so that we can do better that must be a 9 this is a 9 over there 9s these nines mean that's a 9 as well which means that's a nine that's a nine that's a nine so the nines are now I think they're done so that's useful starch just 7 s 6 s can be pence marked into one of those squares because of these sixes look so only 1/4 in the grid with two fives they do interact down here that may allow me to lock a 5 in to one of those squares and u18 as well now that 3 that 3 is interesting is that 3 rules out to 3 from those two squares now you may say are but that's not useful because you can't pencil martha threes you're quite right but if we notice those threes now in this top right 3x3 book a locked into column 7 and column 9 now if we scan down the grid the threes are locked into the same columns column 7 and column 9 in this bottom right 3x3 block so the key here is to realize that we mustn't therefore focus on column 7 and column 9 anymore they've already got all the 3s they can possibly handle we need to focus on column 8 + R square a3 can go you know it can't go here we know it can't go in either of those two squares so it must go in one of those two positions which actually isn't useful or [Music] now I don't think it is useful so I was now so I'm now been scanning these blocks to see whether I can map the threes to exactly the same rows but I can't so we've got a sink again now look though this three had an effect over here this one is exactly the identical effect down here rules out one from those squares so the one must be in one of these three positions and look that matches up exactly with the bottom light box so we now know the ones in this box and the ones in this box are locked into row seven and row nine therefore the focus needs to be on row eight where can a one go can't go here can't go in either of those squares therefore we get some pencil mark once and look and smart ones here and some art ones here so in column one and column two we've located the ones if you like therefore in column three where can the ones go can't be here in here can't be here in here because of the pencil marks so must be in one of those two positions and there's a one there so that's a one and now those ones being that's a one therefore that's a one now now this is another good reason for using pencil marks let's look at the ones and the threes in ten and the fives and the twos we're going to get a flurry of activity here because if I know that a pencil mark means a number can only go in exactly two positions in a box then once I eliminate one of those possibilities I know the other possibility must be true so here this can't be a one because of this one therefore this must be a one and the moment I place this one I'm taking the position of the three therefore that three is going to have to be true the moment I place this three that five now must be true and the moment I place is 5 2 must be true true we get a big flurry of activity and that's why these are one of the reasons these pencil marks are very efficient now these two squares the yellow squares here must be seven and eight to complete this block it's a seven there look so eventually we can resolve that that must be a seven there's been eight I know the sevens over there ah now we've got two eights in the grid so there's an eight here and then they here what can we do next four must be a four in one of these two squares ah yeah okay so where can a to go in this column now that's a two here look a 2 here and a 2 here so there's actually stop my highlighting but ah sorry there's only one place a two can go and that's that one that's a 2 that means that's a 2 that means that this square must be up to this these 3 2 is interacting the moment I place that 2 that means that must be a 6 and what's more that there's two twos there so there must be two in one of these two squares so these two squares are a two five pair these two squares must be a four eight pair so that must be a pants before therefore this now an eight in one of those two positions up here because of these aids this muscle fitness me this must be a 1/4 pair this is a 7/8 bear and can we go can we do next that is the question 3 4 & 6 to complete the central row of the grid that one look that sees a 4 and a 6 in the column so that square is a 3 that one must be a 3 don't have to think about it just immediately see the pencil marks and unwind them these threes those three here forces a 3 there now that must be a 3 up there and that's actually that's nice thing to note so the moment I spotted this 3 I'm actually scanning down this column why well the reason is that any number in this column that hasn't appeared in this box yet has suddenly been made much more powerful by this 3 and look at this 7 so now I actually get to pencil marker 7 which I couldn't have done before this 3 was in the grid now let's see if we can do anything with that so well yes we can actually that's good now the 7s here let's look at this column where can a 7 go in the column well it can't go here anymore because of these pencil marks sevens it can't go here because of this 7 there so it can actually only go there so that's a 7 that's an 8 this means that we pencil mark sevens here this eight means there must be an eight in one of those two squares and now look these eights this pencil marked eight can no longer be true so it's friend up here must be true in the moment I place that square lots of things happen firstly I get that seven which means I get seven above it as well this square must be a four to complete column this is a five eight pair to complete the box and down here I must need a four I think to go along with my six to complete this box right so this is a four or a six that means there's a five in one of those two squares I think that in five in one of those two squares because this five down here check this column that's got to be a four or five doesn't it to fruitful actually those of you who enjoy you neatness might notice this arrangement with the twos in the fives I can't be a five in either of those squares there is a five in either of those squares the puzzle is broken and you can see that because this would form a deadly rectangle if this was a five for example in the finished solution then we would see a five here a 2 here and a 2 here and the problem with that is that these would form a pattern where you could simply shift the five into this square that would make that a five that or two and that a two and there's no way of knowing which of those solutions was the correct one of course the solution in the printed on the printed page might tell you that the fire was there but the puzzle itself doesn't tell you it's there that's just an arbitrary choice there's nothing in the logic that would determine which way round they should go and that is a sign of a bad sodoku so if you start seeing that in your puzzles you need to change your app or look for different things now if we look at this column and ask where to fork and go look there's four over here it's very helpful that's a four that's an eight that's a five now therefore that should be made up here now that sees this pencil mark so that's an eight that's innate that's a fine yeah we couldn't we could use uniqueness to force the five up here and therefore the five over here now I'm not going to do that but I will fully appreciate that ice a completely valid way of approaching speed solving this if that is your preference this must be a six now it's a six into one of those squares so I'm just trying to see an elegant way of not using uniqueness to take this yeah here we go there's a 6 here and a 6 here so that's gonna look a 6 into those two squares so now we know there's no 5 up there so the fives are up here which means this is a 5 means that's a 6 still need 1 4 and 7 into these squares so again if you wanted to you could note that it's not possible for there to be a 4 in either of those squares or again we'd have a problem with the exactly the same in exactly the same way we'd have had a problem with the twos in the 5 to 6 here that's just a bit better that for us has been staring in the face for the last five minutes or six there therefore this should be a six I think that was also 602 that sorts of two and the five that resolves that five that seven that's seven must be true now therefore that's a one that's 4 that's a 4 that's a 1 and that should be a 4 I think that should before and that should be a 5 and that's how to solve that puzzle so yeah took it a bit easy made a bit of shank at the end by not noticing that the top rope is all but complete but I still think there was some interesting stuff there and as a safe do let me know if my microphones better I'd be interested to know thanks for watching and if you enjoy the content please subscribe please give us the thumbs up we really appreciate it back soon with another edition cracking the cryptic [Music]

Channel: Cracking The Cryptic

Views: 42,327

Keywords: hard sudoku tips, hard sudoku tricks, hard sudoku playable, hard sudoku free, free sudoku, #sudoku, sudoku lessons from the pros, sudoku expert lesson

Id: f7sYMtsaUcM

Length: 15min 28sec (928 seconds)

Published: Sat Nov 02 2019