Extreme Sudoku: Finned Fish, XYZ Wings And Empty Rectangles

[@sandpiperbf9767]

Wow, this is probably one of the trickiest puzzles I've seen you do.

[@jrbr549]

@ 12:44 you state that a 6 can only go in C 8,9 of row 5. But you have a 3,6 pair in col 1. How did you eliminate the possibility of a 6 in c1R5?

[@bryantretheway3809]

I know this is old, but i'm wondering the same thing!

[@christophejefferies522]

I think he misspeaks - a 6 could also go in r5c1. (He then uses this as part of the finned x-wing.)

[@kevinbrouelette6361]

This Is why I support the channel :) Nice solve Simon.

[@unexpectedparolemadwerewol6565]

6:43 , row 8 was 1,3,5,6 needed as you called out. Column 2 crossing that had the 1,3 and 6. located your 5 for you which in c2 r8 allowed solving column 4 at a minimum. but great stuff. I'm learning a lot.

[@leroybullied7705]

It seems to be easier to pick up on their misses than it is to see our own when we;re doing it.

[@rabidsamfan]

When I have to change notation I switch over an entire 9x9 square at a time so I don't have to guess at whether I have done a specific cell yet or not.

[@debralegorreta1375]

The empty rectangle did it. Well done, Simon.

[@imransaifi2399]

Thank you Simon for solving this sudoku for me.

[@cadmar2969]

Both enjoyment and learning at the same time from these difficult puzzles!!!!

[@rickwoods393]

you said 1356 on row 8 column 2 that would show a 5 could only be there

[@cadmar2969]

@@rickwoods393 yes. a hidden single. 5 is only number can go in

[@haydenhoodless2055]

At 24:00, I could not follow the logic, but isn't there an X-Wing of 3s in collumn 3 and 8, which is why you can rule out the 3 in r1c8?

[@lydiag785]

In the places where the 6 X-Wing is, is there also a X-wings with 3s? Which would solve the 8 in r5c8 for the same reason? Also not sure what qualifies r5c8 as a fin and not r6c9, or is it interchangable?

[@mohameddib6069]

The empty rectangle... very clever

[@Ghaz002]

12:05 yeah people like me... this is where i lost it lol

[@joeroberson6676]

I am wondering like Jrbr did one year ago. @ 12:44 you state that a 6 can only go in C 8,9 of row 5. But you have a 3,6 pair in col 1. How did you eliminate the possibility of a 6 in c1R5?

[@pythagoras2001]

Very nice!

[@CFCNOTBUMMER]

I can't work out the 5 in column 2 at 10:10, can someone help me please

[@CFCNOTBUMMER]

Sheesh, it waas so obvious I was over thinking it and , please ignore the dullard

[@pedrolopa2]

what is a "deadly pattern" at 3:50 ? I don't follow the logic ? Is this pattern impossible on any solution ?

[@leonardosoteldo9542]

It will nullify the puzzle, because you it will not have an unique solution. You would not be able to know which number goes in which cell. Sudokus can not have to possible solutions, so you can discard the possibility of that pattern.

[@murphy9453]

I understand the uniqueness and that this cannot work. What I don't understand is how you know to eliminate the 1 and not the 5 and from Row 6 and not Row 3.I am sure it is obvious, but I don't get it. Thanks.

[@christinebuckingham2480]

Would it not be easier to use the marking software that allows you to put the only numbers that can be in that cell in the middle? Is this a video before they came up with that software?

[@MisterM2402]

Yeah, they use their own web app these days which has the centre notation (and just looks a bit nicer too). However, they used to only use the one in this video, I think it's called Duncan's Sudoku Solver?

[@myron162]

Wonderful work Simon. I'm just a bit confused about the uniqueness problem... Columns 1 and 9, rows 5 and 8... The 3/6 pairs did not resolve the uniqueness problem as I saw it. Or is it acceptable as each cell was in a different 9x9? EDIT: Never mind... I caught it. If the 3 and 6 were switched in column 9 the left center 9x9 would have two 3's. And the right center 9x9 would have two 6's with a column 1 switch. That's why you're the champion, Simon, and I'm not.

[@skurinski]

I understand the uniqueness and that this cannot work. What I don't understand is how you know to eliminate the 1 and not the 5 and from Row 6 and not Row 3.I am sure it is obvious, but I don't get it. Thanks.

[@עפריזאקמן-מ2ב]

He knows that the 5's goes into r5c79, so i 1 will feet in these also there will be 2 sulotions, therefore he can eliminate 1

[@Decco10000]

For the dullard can you explain why a2 is not an option in r4c7?

[@CrackingTheCryptic]

Have a look at the trick I go through starting around 18m45s into the video. If it still isn't clear, let me know.

[@absrenato]

Is there somebody that could help me, please? At three minutes, twenty seconds: Simon says that the number 1 can´t be placed in two specific cells in row 6. And it gets worse: he also states that the combination of 1 and 5 cannot be placed in four cells nearby. As far as I can see, the number 1 could be put in the SIX top and bottom cells, exception made only for the central row.

[@DougalAAllan]

The issue with having four 1/5 pairs arranged like that is that at the end of the puzzle, even after filling in each and every other square, you would be left with those four squares being marked as 1 or 5 and having no way of knowing which was which. You would be able to mark them as 1 or 5 and it would still be valid. "Uniqueness" means that in almost all hand-crafted puzzles there is only ONE correct solution, and this situation where those four squares could be a 1 or a 5 as you see fit and therefore having TWO solutions will not be valid. This allows Simon to eliminate the bottom pair from having 1's.

[@absrenato]

@@DougalAAllan, thank you so much for your time. I am working on it and realized what uniqueness is, a new concept for me. But in my mind the trouble still remains: the number 1 could be placed, in the bottom row, in the middle column, for instance. Unless...Oh, think I´ve got it! He says that those TWO cells can´t have the 1. Only those two, not the line. Thanks again, pal. I guess I have much to learn.

[@richardwagner7758]

I'm in the dark as to why (C2; R5) is called a 4. the double 4 was c2;r4 and c2;r5

[@saintkakuja]

yay

[@jixigg]

Wow

[@Decco10000]

Sorry to be the novice here - but why call it an “empty rectangle” when one of the 4 boxes highlighted in this square-shaped [2x2] “rectangle” has a 9 in it?

[@CrackingTheCryptic]

It's because the "empty" part is saying that there is NO 2 in the rectangle - not that there is no number at all in the rectangle. It is the lack of a 2 option in any of the squares in the 2x2 "rectangle" that means we can do the logic shown at around 21 mins into the video.

[@berldon]

Still can’t follow the logic why R6 c7 and R6 c9 can’t have a 1

[@chanfranc]

Uniqueness problem - the final solution cannot have (a) 5 in r3c7 and r6c9 AND 1 in r3c9 and r6c7; NOR (b) 1 in r3c7 and r6c9 AND 5 in r3c9 and r6c7. If 1 occupies either r6c7 or r6c9, it will cause one of the situations (a) or (b), and the puzzle would be invalid (i.e. solution is not unique).

[@robertjohnson3011]

It looks like an X-wing to me since I don't know the final solution at this point, so what information already known rules out both of the X-wing possibilities?

[@chanfranc]

@@robertjohnson3011 Yes, it is X-wing for 5 but not for 1 (because r6c7 can be 1, 5 or 6.). But this is NOT the chain of thought to get the solution here. Please think of it this way: If the final solution has 5 in r3c7 and r6c9 AND 1 in r3c9 and r6c7 (case a), do you agree that by exchanging the two 5’s and the two 1’s in this final solution (i.e. you get case b), you will get another solution which will still satisfy the rules of Sudoku? If you understand this point, you will understand the meaning of “uniqueness problem”.

[@robertjohnson3011]

I see it now. r6c7 and r6c9 are the only available places for a 5 in that 3x3 block. Thus, if one of them were a 1, the other would have to be the 5. Same if either is a 2, but IF they were 1 and 5 in some order, then r3c7 and r3c9 would be 1 and 5 in the opposite order and any other square on the board that could see one of those 5s could also see one of those 1s regardless of which 2 were the 5s. Thus nothing else on the board would be able to constrain those two 1s from trading places with those two 5s and the puzzle would then have 2 possible "solutions", which is not allowed.Now, that's sophisticated logic!

[@vincentangwyn2144]

@@robertjohnson3011 but i do find an application a long time ago that confuse me by giving sudoku that had multiple answer, so i thought uniqueness is not really rule.

[@pacman52280]

I didn't need any advanced techniques to solve this. Just basic logic. How? By placing every possible number into each empty square in the grid first and then it was a walk in the park. I would grade this puzzle as beginner easy.

[@antono.8896]

Yeah I used to do that as well, bruteforcing it. I guess thats always kinda easy, but I think your not improving really using this, keeping yourself at a limited speed and understanding.

[@pacman52280]

@@antono.8896, I don't care about speed when solving sudokus. It doesn't matter to me if I take 15 minutes or 2 hours to solve, as long as I solve it. I am currently working on a monstrous sudoku with 25 interlocking grids where there is a 26th within which is clueless. I first started working on it a couple of years ago and I work on it off and on, mostly off. Still not even close to finishing it.

[@eldaralex3067]

@@antono.8896 true, it's about breaking a code or a safe by using a pattern, like discovering a special way to the source and not about trying every brutal and vapid cambination or hitting every road until you don't meet a dead end, it would be a really tiresome and boring trip for me this brutal force. And the worst is that you don't learn anything else ... is just the same "brutal pattern" on an on. Not here to say how to play sudoku, as long as you like it, enjoy it. I myself enjoy the hidden beauty of it.

[@ronmasters751]

Hmmmmm … not a unique solution.