Extreme Sudoku: Chains, Chains And More Chains

We take a look at a puzzle requested by a viewer. This is a completely insane puzzle - hence the length of the video. Apologies but we did want to try and solve it logically.
We would be very grateful to any viewers who might consider supporting us by becoming patrons of the channel on Patreon. Our page can be found here:
/ crackingthecr. .
If you have a puzzle you'd like to see us solve, please either email or tweet it to us at:
[e-mail]
or
@crypticcracking
#crypticcracking
#sudoku

Great to see how you get into a sweat and still come with logic to the solution. That was one of the best episodes so far. Thank you, I love your Sudoku videos ... Greetings from Berlin. Thumbs up!!!

I watched this video again and I'm excited again. Of course, as I have continued practicing and watching your videos over and over again until I understand the logic, I am now familiar with the techniques you mostly use. But it's so hard to discover what the next step is. Great videos ... !!!

[@faithwlkr]

This was an excellent video! It was so helpful to hear you talk your thought process out loud. Thank you!

[@telduf1]

Hello Simon - brilliant perseverance on clear explanation of chains. One of the very best sequence of logic I have seen on a channel. Vert well done

[@faithwlkr]

This was an excellent video! It was so helpful to hear you talk your thought process out loud. Thank you! I would love to hear you talk out loud even more for those of us novices tuning in.

[@cadmar2969]

Excellent!! Love these challenging ones!

[@calmeilles]

HoDoKu classes this one as "Unfair" - which seems an entirely reasonable judgement. :)

[@leojf3828]

I love the chaining technique. Especially logic that proves a contradiction.

[@jimdetry9420]

Shortly after 20:00, while messing with the 1.3.7.9 you forgot to put the 2 back in R1 C2. As it turns out, the 2 wasn't there at the end, but I think you got lucky.

[@qazwiz]

grrrr you're right, i thought i noticed a quad he missed (1379) which would have placed 5 at the 5-9 and cleared the 1-2-3-5 as the 2 but since he forgot to replace the deuce it only LOOKED like he was skipping a quad (but he DID go many minutes without noticing)

[@leojf3828]

Yeppers!

[@thomaswilke6312]

This is an excellent tutorial!

[@crazypomp927]

Man I was going nuts seeing you put a couple invalid 9 pencil marks in there. Just yelling at the screen at a few points

[@lordjecht]

@17:50 that was great how you eliminated 1 & 3. You just missed the 9 and you could have figured out that only 5 goes into that square.

[@arnevdamme]

My thoughts exactly!

[@TheEricthefruitbat]

I consider this to be a bad puzzle. At the point where you are examining several large chains, it really becomes little more than solving by (educated) trial and error. That kind of inelegance is not satisfying, for me. Well done on cracking it, but was it enjoyable?

[@nj3390]

I sent this hahaha amazing. thank you!

[@JustFun-iz9rf]

Well done

[@rabidsamfan]

That was a real tough puzzle. I had to bifurcation twice before it gave up throwing curveball at me. I wonder how Mark would approach it.

[@lawrencekallal6640]

Starting at 9:00 there is nice forcing test solution that will crack open this puzzle open. Whichever of the 2 positions is chosen for the 6 in the top middle 3x3 block, the 2 in that block gets forced into R1 (RC16). One of the 6's position directly forces it there, and for the other position one just needs to follow a couple of forced 6's around and note where the 2 gets resolved in the top left block (RC31). Resolving this 2 opens up a relatively easy path to a solution. The 5 in the top-left block gets forced into RC13, which in turn resolves the 5 and 8 in the left middle block, leaving only a 19 pair left in that block (RC 43, 62). Finally, if the 9 is chosen for RC43, following the forced 9's around you end with no place for the 9 in the top right block, so that square has to be a 1. With the 19 resolved in that block, the puzzle is easy to finish from there on.

[@chrismoyler]

Trying v hard to follow your logic. Can't see how the 2 is forced into r1 Tky

[@lawrencekallal6640]

@@chrismoyler First case, 6 in RC35. The 4 gets resolved to RC36, and this bumps the 2 in that block to RC16. Second case, 6 in RC24 … 6 in bottom middle block to RC85. 6 in bottom left block to RC93. 6 in top left block to RC32 for 67 pair (bumps the 7 to RC12). With the 67 resolved in the top left block, the 2 only has one spot left -- RC31. This 2 in turn bumps the 2 in the top middle block to R1. Either case for 6, the 2 in the top middle block is in R1 (RC16). With the 2 in RC16, the 5's in that block have to be in R2 -- this resolves 5 in top left block to RC13.

[@NMalteC]

Great puzzle! At 8:35 you could still have placed pencil marks for the number 7 in rows 5 and 6 and eliminated the 9 from the 139 in row 1 column 5. That would also put pencil marks for the 9 in the South block, column 6 (you found that at 31:00). Also, pencil marks for 5 in the West block were possible. I'm not sure all of this would have helped speed up the solve of this puzzle (the most difficult puzzle yet on the channel?)

[@pedzsan]

I either don't see what you see or you see something I don't see. At 28:42, I think there should be a 1 candidate in R2C1. You have just 59 as candidates and it seems like it should be 1589. I don't see why 8 or 1 have been eliminated.

[@andrewdstokes]

I'd love for you to add links to your modern solver app for these. the old Duncan's solver drives me mad with the inability to show Snyders and locked combinations in the cells!

[@travisbaskerfield]

He missed a quad in row one for the longest time which placed the 5 and 2 much earlier if he'd spotted it.

[@cardguys]

Suggestion: only put in small numbers when all small numbers are known. Then work backwards to eliminate small numbers. Suggestion 2: name rows columns and sub grids alphabetically rather than numerically.

[@stanvandervoort2240]

@20:49 If you look at row 1 you can eliminate the 9 from the 3th cell because of the 1,3,7,9 quadruplet in the top row. That pretty much solves the puzzle.

[@hellstorm42]

Unfortunately, you couldn't do that since r1c2 could still be a 2. He removed 2 as an option while demonstrating a chain at 19:55 but never put it back. He got lucky that the removed 2 didn't backfire

[@lsmart]

At 13:55, pointing to grid1, Simon says, "It does seem like this box is where we ought to focus." Can anyone explain why he thought so?

[@gordieranger]

Impressive solve! Spotting the naked quad in row one (1379) would have given you two easy numbers though I don't know if that would have been enough to crack the puzzle

[@wojciechkaminski7378]

Hello, I recently came across your channel and I just love the way you explain the logic and techniques - it's addicting. For this particular puzzle, I am wondering... @ about 17:10 when you filled in canditates for R1, I thought about quadruple being at C2,5,7,9, which would immediately give 5 and 2 in C3 and C6. This assumption later turned out correct, but I'm thinking if at that point (filling in candidates), the assumption of quadruple was warranted, or was it just my lucky guess?

[@michielgerretzen9777]

@18:30minutes into orbit: After proofing that cell (1,3) can't contain a 3, it follows immediately that the 3 goes into cell (3,3). With a 3 in column 1 and 2 and the 6,8 pair in column 3, 3 in box 1 can only go into cell (3,3). I don't see the benefit from showing first that neither a 1 can go into cell (1,3) ..... (for sure it's me :-) )

[@lc8226]

Thanks

[@CrackingTheCryptic]

Thanks L C , we really appreciate it. Simon & Mark

[@goldenera7090]

brilliant solve with 1,3,7,9 @20:00 min. @ 29:52 can we use uniqueness and say L there can't be 1,7 in row 1 col 7 & 9. hence it gives 3,9 double in those cells and row 1 col 5 is 1... nah that doesn't work... so we can't use uniqueness??

[@christodoulostsilopoulos7932]

Thanks a lot for the tricks you show. Can you tell me which is the software you use for solving the sudokus ?

[@CrackingTheCryptic]

Yes, it's called Duncan's Sudoku Solver (just type that into google and you should find it!).

[@hargrim6892]

36:35 is it a lucky guess? 🤔

[@flyingwombat4884]

no, it was not a lucky guess. This cell has to be a 1 because it sees numbers from 2 to 8 in box, column and row

[@Blubb5000]

26:40 How in the hell do you find these multi number chains?!?

[@RowenaBach]

Just starting to learn sudoku, I don't understand how you knew the first 2 R7c8 and first 5 r6c5 went there. 😳 any advice or tutorial videos on that?

[@moshehim1000]

36:35 - How did you figure cell r8c1 is 1? I mean, it really is, but at this time, cell r9c1 could also be a 1, couldn't it?

[@flyingwombat4884]

This cell has to be a 1 because it sees numbers from 2 to 8 in box, column and row. Also If r9c1 would be a 1, then what number could you put in r8c1?

[@ols1012]

You had 1379 quad on row 1 you missed that

[@khayman9574]

I absolutely despise chains! If this is x then that is y and the other one is z so, therefore, the highlighted square must be Jesus Mary and Joseph with the Holy Ghost on top. It's a process of trials and eliminations that still defies my profane understanding of the game. I want to be able to solve a sudoku with logic and techniques but, hey, maybe I'm just useless at this stuff? BTW, I couldn't solve this puzzle, obviously; in fact, even the Android app I use told me "Sorry, this puzzle is too difficult to be solved by the built-in strategies alone"... and it has a Godzillion of them, many of which I'm still unfamiliar with. 😩😩😩

[@md.irfankhanfahad6870]

10:41 how did u eliminate 6 fron c3?

[@lsmart]

The only 2 possible locations for the 6 in c2 are r2 and r3. If the 6 is in r3, you have an x-wing, which eliminates the 6's from all the other columns in r3. If, on the other hand, it is in r2, it still eliminates the 6 from c3. So either way, there is no 6 there.

[@christinebuckingham2480]

Why not just go through numerical to get all the numbers you can to begin with?

[@jimjimellell]

That's how I do it, but I start with cells that have only 2 possibles. If that yields no results then I ink in cells that have only 3 possibles, then 4, then 5. I always start with 1 and work up to 9 so the "pencil marks" are always in numerical order. That makes it easier later on . I also put the possibles at the top of the cell, and the "not possibles" at the bottom of the cell with a minus sign. That helps later on too. The link to the online puzzle puts the possibles all over the cell in no numerical order and no option for "not possibles". So I write the given digits onto a blank Sudoku grid and do it my way. It might take 2 or 3 hours but I always get it done without the "esoteric logic"

[@TheKingsOutlaw]

Why couldn't the X-Wing on 6's eliminate a 6 from R2C3?

[@mikeoxmaul9386]

Because it could only see the fin, it wasn't in sight of both the x wing and the fin

[@paullaurance1991]

Been trying to improve and have been looking at some of your videos. A little disappointed that you left your "just-the-pairs" technique before you'd looked at them all (eg 5s in r4c3 and r5c1, 7s in r5 and r6). My natural technique always takes me beyond just the pairs, so seeing you move on to 3s so early was disheartening. Anyway, keep up the good work, and I'll keep learning.

[@bbsingh8159]

Could not solve, failed.

[@shane8037]

absolute garbage... if the solution requires this kind of mindless brute force (that's all chains are) then the creator should have binned the puzzle, not published it

[@martinpolach6171]

I agree Shane.....lacks grace and eloquence....grinding, grinding...eventually water will wear down the rock....