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

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.

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

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.

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

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...

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

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!

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

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.

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.

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.

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

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.

I, obviously, can't speak for everyone, but when I catch something you or Simon miss I am most certainly not triggered. I am elated, because it is such a rare occurrence.

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

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.

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.

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.

Super helpful! I appreciate more of an explanation of what Snyder notation is. It's been referenced but I've had a hard time nailing down what specifically it is, so that was really helpful. Also appreciated the tip about using pairs to deduce other parts of the grid. Always learn something new on this channel. =)

Fascinating. Thanks illustrating your either/or technique for bivalue cells Mark. I find them to be quite powerful. I can always get out of a jam by testing them. I tend to use them at endgame when all else fails, but now I realize I can use them mid-game as well.

I'm 44 seconds in to the video. Yes! Exactly! Thank you! I found you somewhere early in the shut down. No idea how. Became addicted. Went full Patreon. The next day tried your methods. Rethought patronage. Let's do this!!

Great channel ! I discovered you by chance a few days ago and you made me realize that Sudoku can really be thrilling !

For those new to Sudoku or are stuck at an intermediate level, these sort of videos are absolutely essential. Thanks!

This was my first and only hard solve and I did it in about 1hr and 20ish minutes. Before this I had only attempted hard and had only solved a couple of easy ones. By watching this channel for about a week or two, now I felt like I was able to do some logic which I was not able to do before no matter how hard I tried. It was not obviously at the level shown in the vid. But I am still happy to be able to solve this on my own.

Thanks for this video learned something new with that chaining link. Very helpful.

Several months ago, you presenters as well as some high-profile setters in the comments turned me around to the idea of using uniqueness as a logical method. We've recently encountered a sudoku where that's not the case, but that was a very special case, I'm sure you know what I'm talking about. So I was actually perfectly prepared for you to use uniqueness and accept it. But THEN, you turn it around again! And for some reason I'm super happy about it!

I very much enjoyed this video! Im happy that you bring the explanations down to my level and take your time explaining some of the concepts (particularly the uniqueness bit)

These have been really helpful, thank you!

The precious one! Two powerful methods I did not know. Thank you very much!

I like these classic sudoku technique videos. I've learned quite a bit from these.

Thank you, your cracking of the 3 and 7, and then the 7 8 and 9 was excellent. Enjoy your even pace reasoning and clear illustration.

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

I just started getting reinterested in sudoku after remembering how my math teacher would make us do a puzzle to start off class lol! It's super helpful to hear you think out loud, I didn't know about the Snyder notation, but will definitely start using it!! Great video, much love!!!

First video to watch on your channel and I can follow your great logical talk through. New subscriber. I’m away to look at another puzzle. Thank you sooo much. 👍. 🐢

Very helpful! Thanks for this.

10:12, completely missed that, ended up making a chain completing the puzzle of that cell was a three. Worked out every candidate trying to find an error and it turned out to be the final solution. Took me 40 minutes.

Thanks for this very informative video! Managed to solve this one by myself first thanks to watching other videos on your channel. So it was interesting to then watch your solve and compare my results.

Brilliantly solved with good teaching

Using uniqueness is a perfectly valid way of _solving_ a puzzle, but (like bifurcation), it solves at the expense of appreciating the beauty of the logic involved. As you guys highlight the beauty of these puzzles rather than merely demonstrate the quickest way to solve it, I really appreciate that you refrain from using uniqueness.

Hi, thank you, very helpful and feasible, great lesson!

I agree that it's harder to spot things when you fill every cell with all possible values it could have. So I'm limiting my pencil marks to 2 (max 3). But that chain inference placing 3 at R8C6 that started at R7C2 with 3and7 as possible values is mind-blowing. I will never spot that ever.

You are a great teacher. Thank you!

I really enjoyed the deductions, thank you Mr. Holmes.

I'm new to this and I do mean new and this is really helpful in getting an understanding of the process involved, many thanks.

Thank you. You've given me a new way of solving the puzzles.

I love watching this channel, it makes me feel like a genius as the puzzle is solved before my eyes hahaha

A great learning experience for me. Thanks

That was fun to watch! I like your style of teaching.

This is so helpful. Thank you

I enjoy watching. It has helped me and has changed my approach to solving puzzles

Thanks for the how to crack expectation really helpful

That was a masterful lesson in how to make the difficult look easy, thank you. Is the technique you used two times equivalent to the XY wing technique? Either way it still needs much practice to spot these possibilities.

having watched your videos again I can now feel confident in my skills

I had fun solving this one in under 30 minutes. I did use a (different) uniqueness test when I got stuck at about 20 minutes. Thanks to Cracking The Cryptic for teaching me about that possibility! ;-)

Amazing video and puzzle, great tips. Thanks !

Thanks a lot! I love watching your videos❤

Great Job and very informative! I learnt a lot! Thank you so much!

Thank you for this in depth look at your process. I’m new to the channel and had been wondering what you meant by “naked single”. Very insightful!

I love CTC's solving style so much I made a video on my channel where I analyze each step of this solve. In addition to explaining the strategies used, I add a couple of pause the video moments and some alternate solving paths, similar to how someone analyzes a chess game.

This pandemic has brought me to this channel out of nowhere and i can't stop watching. Absolutely brilliant!

2:40 I use a dot or point system where I poke a dot at the position the number would have in a 9 digit grid per box. So if a cell has a potential of being a 6 or an 8, I would place a dot on the horizontal center axis to the right to represent a possible 6 and another on the vertical center axis at the bottom for the 8 position. In many cases I get to the point where deduction cannot eliminate options to a single option and therefore guessing between possible option 'A' or 'B' (eg 6 or 8) is a wild guess that can give progress until the knot occurs and then there's no going back.

I wondered a couple of times why you guys avoid the unique solution, so thank you very much for explaining! :) For myself I just figured out that it is harder to spot, when additional rules apply. For example a knights move could solve the double 79 pair and it would have been a mistake to say it is a 4 because of uniqueness. Thank you again for the explanation :)

Thank you I really learned a good technique

You are absolutely fantastic. I love the way you solve

Hi! Do you have any tips for training yourself to become more aware of those chain reaction patterns that limited the three and the seven in the bottom middle square? Thanks! I love your videos!

Thanks for your advice! 2.5 minutes in and I'm wiser already. No wonder these were so hard for me. 👍

This puzzle took me days to solve, even with taking one clue at at time with the video That 3 solution from column 3 really helped, as did the 8 logic from column 3. BOth taught me a lot

By the way, I did like your description on applying logic to the solution for this one. I very much fill out the obvious numbers first and have been known to colour their squares so as not to delete them if I have to clear the cells to start again.

Took me 18:43 to solve; definitely one of the harder classics on the channel. Really enjoyed solving it. As a side note, I've never really agreed with people who think uniqueness rectangles are a non-satisfying, or even, invalid way of solving classic sudokus. Mainly for two reasons, 1. As far as I know (I'll admit that I haven't researched this extensively myself, but I've read it on multiple sites/forums discussing sudoku strategies), while the strategy itself is based on the assumption that 'there is only one solution', even if you're solving a 'defective' sudoku with multiple solutions, using uniqueness will NOT lead to a wrong solution at the end of the road, just one of the multiple correct solutions. In other words, as long as the puzzle you are solving is a classic sudoku that has valid solution(s), there is actually no instance when applying uniqueness will lead to a contradiction, so it's ok to use it. The only case where you should actively refrain from using uniquness strategies is when you're solving variant sudokus; in this case, since classic rules aren't the only rules enforcing a unique solution, applying uniqueness can, and usually will, lead you to the wrong solution. 2. While Unique Rectangles are introduced as fairly advanced techniques on a lot of sudoku tutorials/videos, I actually find that 'classic' Unique Rectangles (such as the example in this particular video) are fairly common and very easy to spot. They can often help out in tough spots, helping to avoid long chains. Again, I'll admit that the same can't be said for 'hidden' or 'extended' Unique Rectangles, but if you're solving a classic that requires these strategies to progress, it's probably an extremely difficult one anyway. Obviously, I understand that everyone has different reasons and styles/preferences when it comes to puzzles, and if using uniqueness to solve sudokus just doesn't 'feel right' to someone, that's perfectly ok. However I personally love URs and use them to solve classic sudokus at every opportunity, and encourage others to do the same.

Great instruction, very helpful to hear t logic

Enjoyable to solve. I find your ap soduku puzzles to be exceptionally hard. Almost all of them are super challenging. Your low level puzzles are harder then 80% of your chess puzzles and some of those are ball busters. But you guarantee I will spend a long time with your ap. Thanks for your techniques here. You introduced some concepts I was not familiar with.

YAY! I actually solved this by myself. Been ages since I last did a sudoku puzzle though the alternative one's really confuse me with all their different rules which I don't even understand most of them but still watching them being solved 'till something hopefully clicks in my brain so I can understand it lol Also loved your comments from 5:10 onwards. I've only just found your channel which is great for me trying to solve them before watching your video to see any difference.xx

Wow, that happened fast! I had to pause and go back to watch a few things over, but THANK YOU!

Excellent, depending more on logical reasoning than on standard formula for elimination

Thank really helped.

Amazing way 😀for solving sudoku 👏🏻👏🏻👏🏻 Thanks 👍🏻

I have found that if you have pencilled in say a 1 in the top left square in column 1 and 2 then it follows that in the two sqares below the 1 will be either in Rowe's 1and 3 or 2 and 3. This has helped me many times.

Nice FT (forcing test) solution with the 78. I tried putting a 7 in RC82 and ended up with an 8 being forced into both RC39 and RC79 = conflict. So RC82 was a 3.

I understand the solution but how you spotted it was incredible :O

I tried to solve one puzzle from past few days. Today I solved it after watching this video. I learnt the way of using the notes. thank u

Found two expert level tricks thankz.

This master solver saying "don't get triggered" has me cracking up! Nice one, man.

Very educative. Thanks so much

if not "uniqueness" then what other technique could be used to solve 3/7? appreciate help!

Excellent chains - I always miss those! :-)

Absolutely fascinating logic: my puzzles will be much more fun! Bravo!!!

Thanks for that. I would never have done this one without your help. Reading the comments I realise I am not very good at all. I do normally manage the NYT hard ones though, so not as bad as I was when I started.

I enjoy your solving. question though at 6:30, could you restrict the center cell to 8 and 9 ? Does not make a difference later on for this sudoku, but I found that is sometimes usefull on other sudokus to restrict 2 out of 3 triplets digits in only 2 cells. this way triplets in line 5 and the center box would be perfect (set of 2 numbers rotating in all 3 cells)

Really good thinking aloud" Mark .. thanks .. the chaining what-if's seemed to be the only way to solve this .. and I'm not very good at that .. so I got pretty stuck .. discouraging .. I use uniqueness just as an impossibility check .. i.e. if I find it is an irrefutable result, I must be wrong .. and need to backtrack .. chaining is not cheating .. but it just feels very brute force-like .. like what a computer would do .. demonstrate conflict than try another pathway .. demonstrate conflict than try another pathway .. repeat ..

Excellent explanation and a good solve if a far from easy puzzle

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.

I learned a lot here , thanks 👍🙂

very helpful - much easier to follow using deduction

I find this really helpful,but still have questions. I would really like to do real life classes, but can't find any. Do you know of any please?

12:30 The uniqueness strategy always works for me. On a page called sudoku academy I never completed the evil level without using uniqueness. (And uniqueness is already hard to use, because it acts as an abstract bridge for a complex forcing chain technique.) It is true that it does not feel good to use it, even when you know it works (it has only failed me in a physical newspaper and on a web page that I have never found again). And also, if you detect a uniqueness but don't use it, it still feels bad because knowing that it almost always works if you focus the other techniques to prove the certainty of said uniqueness, you still took advantage of it in the end.

Thanks Mark, enjoyed that even though I got stuck half way through, at least it's one that normal mortals have a chance with, as opposed to some of the esoteric stuff you've been covering lately.

Uniqueness is a genuine strategy. Instead of looking for crazy patterns that only a genius could see, one can simply use uniqueness and simply solve it. Insisting on the idea that using uniqueness is not pure is BS, because the other harder logic that he finds would simply not work if sudoku was not unique.

2 years later this is still helpful!

I first watched... then I did the sudoku and watch again... makes so much sense. Thanks .. I'm sure I have become a better player . Yes, u r sure not bad for the country 😂😂😂❤