Our Hardest Sudoku And How To Solve It (Slowly!)

One of our "kind" viewers suggested we give this incredibly difficult Sudoku a try. Apologies for the length of the video but Simon's brain couldn't go any faster! Lots of advanced techniques required here including our old friend, the Swordfish.

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[martentje]

Amazing how you spotted the Swordfish and Empty Rectangle with only a few candidates written down!
Also your ability to find chains is incredible.

[brodaqult]

Around 29 minutes I thought you were spending a time thinking.
Then I realised I'd clicked away from a scan popup and had paused the video for a couple of minutes! :D

[michaelbaker]

empty rectangle, swordfish, finned X wing, Y wing, and lots of chains? please don't apologize for such an amazing, well informative video

[timsullivan]

Please don't apologize for delays from momentarily blanking out during "live solves" - by verbalizing your thought progress as you step back to re-assess the solve, you provide a valuable lesson when hitting a brick wall : have I missed something obvious? are their any potentially useful distribution patterns to be spotted? etc. Very useful indeed! Thanks for a great video - learned more than few lessons from this one.

[bryanroland]

I didn't know that some hard sudokus required the solver to look so far along the chain of consequences. I've resorted to starting a chain to see if it breaks but always with the feeling that I was missing something that indicated the next logical step. Anyway, after watching you breeze though some very tricky crosswords, it's nice to see that you're human.
Really enjoying your videos.

[MrKaiAG]

This was very enjoyable! I especially liked the on-screen editing!

[Ruddigore]

Fantastic. These brutal Sudoku's help a lot because you are forced out of all the standard stuff you do and watching how you seek and find the 'get out of jail card' really helps me to tackle and solve those puzzles that in the past I may have given up on.

[SiFuJasper]

Learned a lot from this. I like that you do your standard notations where blocks are limited to 2 numbers, you do not charge ahead and fill in the rest if the numbers. You use logic all the way through. I do all the initial notations as well, but tend to fill in all the numbers afterwards, making my puzzle cluttered, blinding me to X-wings and fishes. I appreciate your channel.

[matthewwestphal]

You, sir, are a Sudoku wizard! Those chains that you did was superb logic and i have no idea how you were able to spot that

[georgesthibaudeau]

Amazing puzzle. I solved it without any pencil marking in 40:37, the exact length of your video ! I spent eons working the potential variations in the lower chute based on the fact the 6 in box 7 was either in the southwest or notheast corner. All permutations always ended up with either a 36 or a 26 pair, establishing the 9 was in r9c2. Also, the 4 always ended up in r8c2. The impact of the 27 in the middle column of box 4 does marvels to separate the right and left sides of box 7 and clear the middle column. There was still quite a bit of work to do, but nothing so complicated. So no swordfish or empty rectangles or other beautiful things for me, but a solution in reasonable time for this difficult puzzle.

[vidyanandsinha]

Yes hardest
Thank you for solving slowly with logical tricks

[sudoku]

Thank you very much for the puzzle! I solved it on my own before watching your video.

At the start, in row 8, once the number 5 is correctly inserted in R8C5, then R8C2 has to be either 1 or 4 and R8C3 has to be either 2 or 4. Although R8C9 has to be either 1 or 8, R8C7 can be 1 or 8 or 2.

My own experience in solving sudoku puzzles has taught me that whenever there's a chance of forming a pair of cells that contain only two possibilities that are identical, take advantage of it.

I therefore immediately assume that both R8C7 and R8C9 must be either 1 or 8. And in fact, my educated guess turns out to be instrumental in enabling me to solve the puzzle reasonably swiftly.

Since R8C7 and R8C9 must be either 1 or 8, then R8C2 must be 4 and R8C3 must be 2. Once this is established, the puzzle becomes quite a bit less demanding.

[TheEricthefruitbat]

I enjoy your videos, and it's nice to see that the techniques I have discovered are sufficient to solve very hard puzzles. I try to avoid "pencil marks" on my paper puzzles, but sometimes they become essential. Thanks for doing these; they are very entertainig.

[wqwwqwqqpoppopoo]

Don't take this the wrong way but I use your videos to fall asleep!

[nigelm]

I ran this through the Andrew Stuart solver starting at the point where you invoked chaining. That solver was forced to use multiple increasingly esoteric steps so I think your approach is well justified. Thanks for this, I’m now realizing that your approach to cracking this one can be a legitimate resort.

[Julesoby]

Thanks for the amazing sudoku. Took me 06:46, that's in hours haha... Did learn 3 new rules because of this!

[coxsj]

It is very valuable to see the overall process, particularly which part of the puzzle to move to when progress is not being made. This vid is also a good example of use of pencil marks and how it can be both useful and can easily get out of control. Don't worry about the length of the vid, some things take time.

[story]

Thank you for showing us. This is incredible and I've learn new techniques.

[jamesking]

2019 Simon: "I'm already a half an hour in", apologizes for the 40 minute video.
2022 Simon: "Oh, you sweet summer child!"

[manrisakirisame]

40 minutes long?

This is gonna be a fun one.