Improve At Sudoku: What To Do When You Get Stuck

[Music] hello welcome back to cracking the cryptic where Kevin yang has sent in this puzzle it looks like it comes from a a phone app and he has tried the puzzle and got stuck when using pencil mark notation so he's actually using Snyder notation so in 3x3 blocks what that means is he's trying to limit numbers to exactly two positions in blocks so looking at this block if we look at where one can go in this block it can only go in two positions and that would allow us to pencil mark ones like that now Kevin's populated this grid in this manner but still not managed to crack the puzzle and he's not sure how to therefore sort of advance the solve is it to go to a full notations method or some other hybrid method so we're going to have a look at the puzzle ourselves if you'd like to try it and please click the link under the video that'll take you to our software and you'll see exactly what I'm seeing and be able to try the puzzle yourselves so let's go must be choosing one of those two squares this one actually allows us to pencil mark ones into those two positions in the bottom right corner and look that then points at this where this can't be one anymore therefore this must be one that's the one of the beauties of Snyder notation is that it quickly allows you to juice juice things like that must now be a one in one of these two squares where is the next easy digit that we can pick off six is look at these two sixes and these two sixes mean this mistresses and therefore the sevens interact that must be a seven must be seven into one of those sevens one of these two splints these are the sudden here and the sudden here eight look this age we don't know where it goes in this bottom right block but we know it's in one of these three squares so we can quickly scan up and where can we put a nut and Ageing this block work can't go in any of these three squares all these two squares so it must go here which means this is an eight now the eight in that square now these twos now operate beautifully on this top left box where can the to go in the top left box will actually only in those two squares and that gives us a one two pair so once we have the same number pencil marked into two different squares like this no we can't put another digit into either of these squares because if we try and put it three for example in this square the implication of the pencil mark logic would be I needed put a 1 and a 2 in this square which is impossible so now we've got a 1/2 pair here so I'm immediately looking I'm looking down 9 here because I can now see that the 9 will be able to be pencil marked into one of those two positions that 59s there as well 7s and some of those where can a forego in this column there's a 4 here and a 4 here there's actually only one position of boredom going to and these two squares must be 6 and 9 and think yeah that's right 6 and some like that like this 6 9 here ah twos here as was that earlier once I've got these twos in here I gives me a 2 into that position and Samak twos therefore into those 2 squares oops 6 here that means like an artifact that's a 6 and those are the 6 down there as well 6 into those two squares ones that come the central blog these two ones here allow us to pencil not ones there and therefore there and when as soon as I got those ones by the way I immediately looked over here I could I don't know where the ones go but I can see they're limited zeros 8 9 now if I could get some sort of equivalence between the ones positioning in the bottom 3 rows I might have been able to do something there but I'm not seeing anything frightfully clever let's check this column because I've got five digits in it and so after this column it's sort of the best it's the most filled column we need one three four and nine so this square is a bit restricted that can only be three or four so I pencil mark in the center of the square there you see this where the corners are being pencil mark that's looking at three by three logic central pencil marking is looking at cell logic it's just looking at this cell and saying this cell can only be a three or four must be three or a nine three nine under six nine here ah there you go now look highlighted two two key digits there have a look at that five seven see if you can spot anything about them and what we need to do is a trick that comes up all the time in the New York Times puzzle this a New York Times hollol this five and seven have actually a profound effect on row six believe it or not because we cannot put a five or a seven in any of those three squares and that is very powerful in terms of row six because especially when combined with this six nine we're running out of squares to put five and seven in to look in column one we have five and seven we cannot put one there either so there we've only left with two cells in row 6 where the 5 and the 7 can go and this this where here where we pencil much too well this can't be it too we know it's a 5 or 7 so that might be important he says and then nothing happens as a result of that logic well actually now one of the things that we can think about here yeah this is cool this is cool right we've got some cool logic going on so once we have a five seven pair locked into a row we can start to think about two different two or three different types of techniques we can think about x-wings skyscrapers and we can think about our old friend the empty rectangle so let's think about it in the context of this bottom line things ringing right sorry Bri fighters had to take phone call but we're about to show you some lovely logic and now we've locked the seven into one of these two squares and we can I highlight those just so make this clear looking at this top left box now this is the key and this is an empty rectangle shape and a key to an empty rectangle it's it's a posh way of saying that a number can only point in two directions in a 3x3 box so if we look at the number seven and where it can point in this box you can see the only possibilities are either that it points downwards or the it points across so there's only two possible ways it's either pointing over here or it's pointing down here and this isn't this is lovely because if it points over this way you can see that in this box where could a 7 go or only in one of those two positions now if on the other hand the 7 in this box points downwards and because we've isolated that the 7 goes in exactly two positions in row 6 a seven pointing downwards in one of these two squares would force this square to be a seven and if this square is a seven the sevens in this box would be limited to exactly one square only this square so we know because of this empty rectangle shape and the empty rec the rectangle in question bizarrely enough is actually these four squares here so it's slightly odd in this this particular instance but the key principle is that a number can only go in two directions like this so we know that there is a seven in one of these two squares we may even be able to do better than that if either of these squares a certain we would know that match of the seven was here but we know for sure the seven is in one of those two squares and so we can pencil mark it and now the seventh being pencil map here is lovely in terms of this box now this can't be a seven anymore and we've got pencil mark seven so we're going to be able to place a 7 here and a six and let's see if that gives us anything extra and you can see is it's going to be helpful for sure it gives us a six here it's one of the things that's going to give us but there's gonna be more I think this must be a six this must be a nine move the cursor out of the way and see this square eyed pencil marked as being a three or a nine well it can now only be a three square now can only be a four same reason this square here can only be a three to complete the row this can only be a three now again that's straightforward said okay because of the three here and this three and we're left with what's in that we need a five in one of these two squares I think along with the nine here we need four and seven so we can cancel marks into those two squares falls into these two squares over here this must be a five which means this this must be seven this must be a five unwinding the pair that we found right at the beginning this must be a five now and this must be a three it's not some threes over on the left-hand side and I'm not certain but it feels to me like we've really broken the back of this now I think that empty rectangle has really helped us I hope I'm not speaking too soon so we need two and eight completes row six now let's do in the 18 and you can see therefore with this eight and this theta factor we can - - one down here this must be nine into one of these two positions we need which we need one two and nine in the central three by three which means this must be a 2 because of the 2 on the right hand side - 1 9 9 5 this must be a 5 now again I want to go too quickly but these two fives and this 5 here on this block force this to be at 5 takes the place of a 2 so we can immediately unwind the pencil marks we're looking for 3 for Nate to complete the box so we got to do this now the 4 here needs to must get 4 and one of those two squares where should we go next maybe have a look at this this column because we've got so many digits in it we need one four and seven well what can this square be I think only a one just we're going to get four four nine seven get unwound yes that must be nine and A three I think that makes this is seven now down here we need a three and an eight I think to complete these two squares don't know the answers to those yet and over here we need a 1 and a 5 all that we can do that's a five and one nut order I'm wearing someone's over on this side look now just place three here that on line 2 3 and the 8th which one why's this 3 & 8 on connait in that square still need a 9 in this blocks and that must be 9 4 that must be 9 and 1 and let's check and it's all good so that's how to do the puzzle now you can see there I used Snyder notation I used this pair forcing a 5 7 pair there and I then once I had these digits locked into the same positions or to two positions I should say in row 6 I was then able to find this pattern up here to unwind I didn't need any extra highlighting I suppose you could say I highlighted the 5 and the 7 which is beyond Snyder notation because that is looking at cell logic so you have perhaps that's the lesson to take away start with Snyder if you get stuck completely do allow yourself to pencil cells that can only contain 2 digits that's certainly a way of finding some of the more advanced patterns so I hope this was a useful video for your solving as I say if you do enjoy the channel please subscribe and really appreciate it and we'll be back soon with another edition cracking the cryptic you

Channel: Cracking The Cryptic

Views: 970,592

Keywords: Improve at Sudoku, learn sudoku, sudoku lesson, expert sudoku tutorial, empty rectangle, hidden pair, hard sudoku guide, sudoku guide, difficult sudoku tips, hard sudoku tips

Id: BnmxrrZUgbk

Length: 16min 23sec (983 seconds)

Published: Sun Aug 11 2019