The Simple Trick For Hard Sudokus

Hello and welcome to Sunday's edition of Cracking the Cryptic and today on screen we have a puzzle that was suggested to us by one of our viewers. This came from Kevin Morford who describes it as his favorite classic sudoku, which is a compliment given that we've probably all solved many classic

sudokus

in our time and this is from a book he owns called extreme sudoku. We don't do many classics on the channel now and one of the reasons is that it's quite difficult to find. really fancy classic puzzles um they tend to do that if as they get

hard

er they tend to almost need help from the computer to be able to solve them and what we and we don't like is we don't want things that require the bingo fork Bowman's or techniques not detected by humans what we want are things that can be subject to cleverness now in terms of whether this puzzle is susceptible to being comical to clever I'll untangle my teeth in a minute um mark has tried this and found it very difficult um, but he knows as well as I do that we're not going to show things that need branching, so I guess this happened to me because, um, yeah, well, it could be one of Mark's little jokes, but it's more There's probably just some

trick

that we need to spot, so hopefully we can do it and one of the things that I think is interesting about this puzzle in terms of challenge is that there are a lot of dice. digits in this puzzle we got nine and two lots of eight, so there are 20 uh 25 digits in this puzzle, so it's well above the minimum for a classic which is 17 and tends to suggest that it might not be too difficult, but we will do it anyway.

Look, you should try this too, obviously, before we start, a couple of things to mention first, our competition to find the best solution for Sam Kaplan lines is brutal. The puzzle is now over, thank you all for submitting entries and congratulations to the hundreds of You who solved this puzzle correctly, absolutely brilliant, we have sent a short list to Sam asking him to judge which one he thinks is the most true to logic which he was thinking about and which also makes the best artistic impression on him. and he will get back to us about the next day in the meantime if you had a

hard

time and want to know the logical path then you can watch the man himself you can watch Sam um solve his own puzzle on Patreon at the moment we have a bonus video from Patreon, we launched it today.

I've seen it, it's very funny and yes, he reveals. They revealed two things to me: first, how smart Sam is to solve such a clever puzzle, but also. When you see extremely smart people talk about difficult things, the fluency with which they do it is impressive, so yeah, I enjoyed watching Sam talk, uh, talk about that sudoku. Now are also happy days if you like our crossword content because Mark has been busy. as you know, practicing hard for the next Times Crossword Championship, which I think will be next weekend, we're doing an online crossword competition this year and Mark has been putting his practice sessions up on Patreon and there's another one he uploaded yesterday, so So now he's made two of these videos.

I think I prefer the first one because he struggled so much with it and it was a lot of fun to watch, but if you like crosswords you can watch those videos. We only have a few hours left. counting the hours in our Kickstarter campaign to create the best sudoku book ever. It's going to be a little sad for us when the end comes, but Kickstarter backers have already unlocked the 27 tick-and-go videos. have us blindly solve the new puzzles in the book, so it should be pretty interesting and I have a feeling they'll even be able to unlock the pdf version, which is what we're offering in the next goal, so it's going to be a project amazing to us, it really is and please support it if you feel able to do so.

I'll put a link on the screen here now in terms of going over the rules of this puzzle today, it's very easy, we just say normal sudoku. supply of rules there, I have done it, so the way to play the puzzle if you want to try it is to click on the link below the video that I can play with, let's start and see how we go, so there are only two on the grid that probably won't be the place to start in classic sudoku I'll just pencil in the boxes if a digit can go in exactly two positions.

I don't have the luxury of three positions or more when I'm doing classics, our two are a little uh look, this worries me, this worries me when these pencil marks are all offset like this and they're not in the same rows and columns , suggests there might be difficulties afoot, I hope I can. I'm not being trolled again, let's move on. The three are very three. All three diagonally here but none of them do anything right. None of them do much of anything useful anyway. Four again. This also reminds me of Derek Neal's slot machine technique, have you ever done that?

I looked at it because all of these digits seem to be offset, by which I mean they don't overlap in a set of three columns that are together like this, you know these four are all out of place and they don't overlap in three rows either and it doesn't do make it easy to spot pencil marks there aren't many fives on the grid okay this is going to be

trick

y uh sixes how many sixes oh we have three sixes again all shifted on the grid look sixes I have to go to one of those two cells , sevens, sevens, all on this diagonal again, all the displaced sevens can be in one of those two positions, wow, and again, one of these two positions, you just know, oh, eights, there are three eights, of course.

We're all made up again Kevin, you're a naughty person sending this here's when people describe classic

sudokus

as their favorites, it makes you wonder what that means, nine actually, a line here for once we can at least we can place nines in the same row in the nine box is that all we get is all we get by just scanning the digits we don't get any digits we don't get pencil marks other than these useless nines in the same row or column um so what can we see? We can see something here, so let me explain what I'm doing right now.

What I'm doing is scanning the digits as I go through them. For example, I noticed these two and these two and asked. the question where can two go and these two where can two go in row column one of the grid, so I see that two can only go in two positions. Now when I see this, my next step is to scan and try to detect. where there is a similar constraint on other columns in the grid, I can lock the two on similar rows and unfortunately I can't, so that wasn't helpful, but that's the kind of thing I'm looking for in the Right now, the other thing What I'm noticing is that the threes and sevens are lining up, um, yeah, okay, so if we ask, that's a useful point, so there's a hidden pair in threes and sevens, I think it's this row down the line. appearance. of things, so if you look at where the seven and the three can go, this three seven discards those two squares, this three seven discards that square and this three seven discards that square, so we know that the threes and the sevens can only go to those two positions and This is called hidden pair because it is not possible to identify it simply by focusing on the cells themselves.

If we look at this cell and ask what it could be and we don't take into account the contents of the entire row, but instead just focus on the cell. You can see that you can eliminate one, two, four, five, six and nine, so this undetected cell that is a hidden pair could still have been an eight, but now it can't be. Yes, something is happening here with the two and the seven too. I think the middle chart is really interesting because look, if you try it and look down the rows and just keep a mental record as you go, are there any patterns that you're seeing repeating?

Now you can see sevens and fours repeating there, so that's it. It's one thing to keep track of repeating fives and threes, repeating twos and sevens, but repeating twos and sevens are really interesting because of the middle frame and not much else, so yeah, when you see this pattern here, it's obviously relevant to rows, you're removing both. and seven from the rows and this two seven here is also removing the two and seven from these rows, so where can the two and seven go in column five of the grid? So there is definitely a theme to this puzzle: the communication between the seven threes and the twos. around the grid, um, now what we really need to be able to do here is use this in some way, hopefully, to progress and again, this is a hidden pair again, so one thing, one thing we should do when we have this.

Obviously we need to scan the column and check if it is being removed. We need to do the same thing on row six, so let's make it so we have one, four, five and nine to place, so this square can only be five or nine. Could you go back and pencil in the options if they can only be a three-digit one if necessary, but let's leave it at two digits for now? David Mcneil, one of the UK's best Sudoku solvers for years and years, always accuses Me of putting too many pencil marks on the grid when I start penciling three things in boxes, so let's please David by being very efficient with our pendulum pencil.

Pencil marks one, four, five and eight here, so this can only be four or five. that's four and five so one can only be one and eight look, this isn't, this doesn't seem to be the trick we needed to get started, oh, it's a shame, because it was very beautiful, ah, one thing and another. Actually, what we should do if we find a hidden pair is important to imagine or observe the effect of the hidden pair in the row, for example, this 37 is to remove three sevens from all open cells, but it may also be important to check It is also in the columns because this square used to be an eight before we discovered this pair, so now the fact that it can't be an eight, no, it doesn't affect anything, but this is the type.

Of something where the removal of an eight from this cell could have been relevant, let's review this, so before we find this pair, what could it have been? It couldn't have been one, two, it could have been three, obviously, it couldn't. It hasn't been four, it could have been five, I think five, five has been restricted, it couldn't have been six, seven, we know that, eh, so for this square it's the 5 that's been removed now, it's very useful , so I'm looking at the column now and saying that the fact that the 5 has been removed from here is useful and the answer is oh no, it doesn't even reduce to a choice of two, it's the same as the eights here. so five is not useful um, let's try the same thing with the two sevens.

We've looked at the two sevens in the column, let's look at it in the row, so before this was removed and it was just two or seven, that could have been it. it could have been one it couldn't have been three four or five the six seven we know approximately one or nine for this square so not being able to be one or nine is very useful no, I don't think that's the case, there just isn't enough of ones in the grid or nines, at least not up here, oh boy, this is not going very well now let's check this one, we have um, so before we had the par two seven, this could have been one four five, let's see. that the two sevens here at least were removed more than one digit from the cell one four and five before all were possible here six eight and nine were not so one four and five were eliminated by finding the pair two seven so one four five can? do something with it those that are not auspicious are like this one ah four oh four four is four is perfect four four these are these four looking at those squares so removing four from this square caused a restriction if we look at row um row eight of the grid Before we found the hidden pair, we didn't know that four had to be in one of the two cells, but now it can only be in this one, so this is kind of useful. um, let's review five too, sorry. while I'm here five is not good five is not good four so I have to be in one of those two we have a digit in the grid well done um no no this was one of the squares that the two of them could enter in the column one we saw this before two could enter here and here, so now the four has taken one of the two positions of two, so this has to be this has to be a two, I think there is nowhere else to a two in that column.

I'm putting it in two, this is going to go, yeah, this will also be useful because not only can I draw two down there now, but look, this two is seeing the pencil mark two, so we get a two here. a two here by sudoku just these two are interacting these two are seeing this so that's going to um well this low this is now suddenly it's getting easier this has to be a two at the top by sudoku so this It has to be a two, this has to be a seven that is no longer two, I think all of the sudden twodisappear into the grid and the seven now look, we can draw sevens down here, but these seven point to one of those two squares where there is a seven in the column and that seven takes the position of a four so suddenly we are cooking with gas here that seven gives me this which means it must be a three there that must be a seven that must be a seven that all the sevens just made fours I have to be in one of those so I have to keep track of the four and three now.

Oh, Forza Falls looks like they're running out of gas, right? So I can see that it's a five pair of nine by scanning column one, so this is a pair of six eight, which means that this square should be, we should be able to understand that, yes, it has to be a three and that three is pointing out that it's a three, so all three must be here. three here three oh yeah three here and wow, okay, suddenly we're doing remarkably well where does eight go in this box? has to go there that means it's one to that means it's one to this puzzle suddenly all these offset pairs have to suddenly become useful um now that means we have to put nine and one here one has to go in one of those cells nine has to go here now um so these two squares could be obtainable if they were to be five and six yes five and six can go in that must be a four that falls four on the top that squares a five or a nine I'm oh no, it's not a five that's a nine that's a five that's a nine these two squares have to be one and eight which we can do the eight goes in eight and six this is six now I'm wondering I'm thinking I'm wondering if Mark isn't He found those pairs because if you don't find them pairs based on the fact that everything we were getting was so strangely offset that I can imagine this puzzle would be an absolute nightmare and he would have just forked it, I know him, that's exactly what What will he have done um and that's why I don't give him credit um now let's take a look down here what do we need come on simon where's your scan? uh it's going to be a four so these two squares are one and five which surprisingly I can't do except this square should be able to get it's just six I think six means it's a six means it's a nine if I trust my pencil marks I always hate doing that if I put them in a long time ago for some reason this shouldn't be an eight it's going to be a five it has to be one that fixes the one and the five the one goes here that should be a check five and here's how to solve that puzzle now what a fascinating puzzle now Kevin, I wonder why this is your favorite sudoku, I think it's because it's very elegant, in fact this 237 is almost a puzzle that you will want to try again without detecting it, just to see if it's an absolute beast.

I'll be fascinated to see the commentary actually, so I have no doubt that there will be some people who didn't notice the effect of this 237 and the fact that you have these three sevens and two sevens as pressure points on the grid if you don't catch them. How monster is this? Let me know. I hope you enjoyed the solution and come back later for another edition of how to decipher the cryptic.