Techniques for Hard Sudoku

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Hi! We're Simon Anthony and Mark Goodliffe, two of the UK's most enthusiastic puzzle solvers. We have both represented the UK at the World Sudoku Championships and the World Puzzle Championships. We're also "cryptic crossword" aficionados. Mark is the twelve-time winner of The Times championship and Simon is the former record holder for most consecutive correct solutions to The Listener crossword. We hope we can help your puzzle solving while also introducing you to some of the world's best puzzles.

Thank you for watching!
Simon and Mark

[brockk]

Today I learned that the best technique for hard sudokus is being a genius.

[glen]

I love these “how to” videos. At my advanced age I’m just discovering Sudoku, and have finally graduated to the hard puzzles. For me it’s so easy to follow the logic while you do it, but still tricky to apply it on my own. I suppose that’s what makes it fun.

[handyb]

Anyone else bingeing this channel? I’m not the best at sudoku but watching this channel is just relaxing

[joek]

The logic starting from 09:20 to 10:00 has been what I have been missing for quicker very hard sudoku times. Thanks a lot!

[YouTubist]

9:30 analysis for placement of the three in the bottom row. Brilliant. I need to add this to my very small bag of tricks.

[B]

what.... I got the exact same grid like him at 9:19 and I got super hard stuck, then he did this with 3 and 7 and I'm mindblown...

[jasonmetcalfe]

Great to see/hear Mark actually explain what he's doing in a way that makes clear sense for a change, rather than purely brute forcing a puzzle open leaving us to figure out what and how he's done it

[tiotito]

9:25 If you're confused here, he didn't do the best job explaining the deduction behind the 3-7 solve. So to clarify, if row 8 column 2 (r8c2) is a 3, that would mean that in box nine, 3 would be constricted to row 7. For now it doesn't matter we don't know the exact cell for box nine where the 3 would go, we can use that row 7 to eliminate the candidate 3 in box eight r7c6. If the 3 candidate in r7c6 is eliminated, that means 3 would go in r9c6. Now if r8c2 is a 7, then in box eight the 7 would go in r7c6, leaving the 3 to go in r9c6. Either way, r9c6 will always be a 3.

[inderbeerkaurjaspal]

I have been doing sudoku for last 4-5 years, I have started loving it, my day is incomplete without daily dose of sudoku in morning newspaper, but I used to get stuck with very hard sudoku sometimes, today I have learned the technique, all thanks to you sir.

[whosyoursaviour]

I love the meta strategy of uniqueness. I've never thought of that. I love situations where you can take outside, seemingly irrelevant information, and make informed decisions for strategy and tactics. I also really appreciate your attitude of pointing that out, and then showing how to solve the puzzle with its self contained logic. Beautiful video my friend.

[kitsurubami]

I've been a sudoku fiend for two days now. Got stuck on an expert puzzle, came here. I don't think I want to do sudoku anymore. Seeing someone who actually knows what they're doing solve in an infinitely more elegant way has crushed me. Maybe another day if I can learn to enjoy it again. TLDR: I thought I was doing sudoku, but I was not.

[ArunIyerS]

As someone who used to work on Sudoku puzzles by filling out all possibilities in all cells and then eliminating them, I can attest to the fact that it takes ages to solve it that way. Also, the Snyder notation that Simon and Mark use have made some of the very hard sudoku puzzles very much accessible, along with speeding up my solves.

As a side note, I can solve almost all of NYT hard sudoku puzzles using the elimination idea very quickly. NYT puzzles come with the auto completion check mark, that I use very often and I find that almost all their puzzles can be solved efficiently by simply eliminating candidates and finding hidden doubles and triples.

[Lebowski]

Fantastic advice: "don't get triggered if you can possibly avoid it"

[umchoyka]

This might be one of the more useful videos this channel has ever produced. Well done Mark!

[bradstrickler]

So happy to see Mark solve a puzzle like this. Great for newer members of the channel, and super great for me who struggles with higher logic issues with tougher puzzles. I aspire to get to the point where I scan a grid, and finds a cell jumping out to me that needs attention.

[PastaFazool]

Brilliant! Ignore the critics, your method is superior. @12:45 Your logic is valid logic, can't have 2 solutions, so 9 doesn't belong in those 2 squares, has to go in r1c3. Again, you're educating all of us, ignore the critics.

[phaustho]

The trick with the 7 in box 8 was my weakness. I couldn't spot that.

[shreyasgokhale]

Very useful techniques showed in this video! See 8:11, 9:18, and 12:31!

[mickeycraven]

Thank you for taking the time to explain how the cells tell off on each other.

[utahgamer]

The handicap of not using uniqueness just makes your solves more interesting to watch. I do appreciate you pointing out when it is available as it is a useful technique that I would not hesitate to use myself. I also find the topic of uniqueness interesting in relation to the star battles and other puzzles that almost require you to use it.