The Simple Trick For Hard Sudokus

[@DonnyTheNerdfighter]

Before watching this puzzle I'd never figured out how to find hidden pairs. I genuinely learned something in today's puzzle. This video should be flagged as essential sudoku learning material.

[@swingasc]

Agreed. I was stuck, then came to his solution, and once he pointed out how to spot a hidden pair the puzzle was cake.

[@banja9172]

Exactly the same here, once he showed how to find 37, you easily find 27 and the 4's in row 7 and that brakes it open...

[@Paolo_De_Leva]

Agreed. Not only about finding hidden pairs, but also about using them to identify possible singles they create in their house (column, row or box).

[@marshallpyatt5425]

Agreed. I need to start working on finding hidden pairs.

[@nickjohnston3763]

@@Paolo_De_Leva j

[@boman2000]

Solved it! Used 2 pencils, a blowtorch, a couple eyes of newt, a rebuilt Flux Capacitor, beef jerky, and a realization that "there is no spoon." Once the owl bobbinsed out of the radio and we filled the tires with pie, we discovered my preciousssss, and the hidden pairs leapt out like dark from night. Easy peasy. Well done Simon, brilliant as always. Marking this for re-watch to learn how to spot those hidden pairs in less than 13 days with a reverse time loop.

[@maryusa8526]

😅

[@lukostello]

His pattern finding skills are off the charts

[@theresalouise1716]

So are his 'getting to the point' skills

[@StorymasterQ]

​What about his 'spotting naked singles' skills?

[@jdyerjdyer]

On naked singles, as long as they give you their digits, why not take them?! ;)

[@GPCTM]

and yet: 18:04 : there's a determined 4 in the 6th box, now; ready to go in. He's scanning 4's. 19:35 : he got it. What I'm saying is: don't be scared.

[@dexterjau3]

Technically they're all on the chart 😝

[@Kuzim1]

I absolutely adore those rare and short moments between "sorry, this is not going well" and "oh, this is interesting". Applies to almost every "classic sudoku" type of puzzle being solved by Simon. My most recent hobby, thanks Simon!

[@anandkulkarni8313]

His pattern recognition skills amaze me. I would have never been able to solve this sudoku without those big hints of hidden pairs. Kudos to Simon.

[@michaelwirth6843]

I wonder if a normal person could solve a puzzle like this if he or she would have played as many Sudoku´s as Simon?

[@BozoTheBear]

"When you see extremely intelligent people talk about difficult things, the fluency with which they do it is so impressive." Pretty much sums up your videos, Simon!!

[@prahas777]

I thought exactly the same thing.

[@956675]

I thought the same when I heard that.

[@kev4241]

The amount of mental organization, grouping similar concepts, and grasping of the essential they have achieved in their struggle is evocative

[@zackvolturo8032]

Is this quoted from somewhere?

[@BozoTheBear]

@@zackvolturo8032 - yes, it's quoted from the current video.

[@DaRaginGamer]

This video unlocked a part of my brain that I didn’t know could be possible. I’m now solving every sodoku in under 10 minutes

[@katecrawford9966]

I just LOVE how polite and kind Simon is - a pleasure to watch you solve!

[@molaeiali]

First digit after 16 minutes, whole video is 22 😅 what a key to the puzzle

[@HalfBakedLunatic]

Yeah, the break in was quite a ride!

[@stevepinard5826]

A Paper Tiger. Never seen a puzzle with such a difficult break-in collapse so quickly and completely. Sadly, I wasn't in the mood for a difficult start, so I let Simon do the hard work.

[@RO8s]

I tried and hit the wall - couldn't find that first number. It's all it took though, the rest was a pussycat.

[@david203]

There may be an inverse relationship between difficulty of finding the first number and the difficulty of finding the rest, and similarly for finding the first k numbers and the remaining numbers. But this would be countered by puzzles where the first number is obvious: in such puzzles the remaining numbers are usually fairly obvious too. And it would be countered by puzzles where the first k numbers are very difficult to find, requiring recursive calculations, because the remaining numbers can also be difficult to find. Summary: never mind.

[@bobhoover1624]

@@david203 p

[@david203]

@@bobhoover1624 q

[@b5fremdet]

@@david203 -(p/2)±√((p/2)²-q)

[@Keldorn01]

My time was 36:46 on this one, and I've got Cracking the Cryptic to thank for that. A year ago I knew precisely zero sudoku techniques, not even naked singles, and now I'm spotting two swordfishes leading to a hidden triple

[@andreaskraft5145]

I did exactly the same thing as you did. When I saw the offset patterns, I straight away started to look for swordfishes. This is also because I have watched Simon solve sudokus here on CTC, especially tattooing sunsets. I think my time was about 10 minutes longer he yours, but I don’t know exactly because my browser reset after my first 20 minutes and I had to start all over again. But definitely a fine time time you got there.

[@MartsGarage]

15 minutes in. Not a single digit placed. Time to see how Simon does it. Edit: Wow. It seems so simple but I wouldn't have spotted it in a million years. Thanks Simon. Oh yeah, nice intro.

[@steviedmrbk5179]

*Looks at the video length* ..."hmm, 21 minutes, I'm havin' a go of this..." 4 minutes later..."nope, nothing!" 🤗🤗

[@FirstLast-gw5mg]

There's a swordsfish on 2 in columns 1, 5, and 9 (2 is only possible in rows 3, 4, and 8 in those columns). Removing the 2 from the rest of those rows leaves two places for 2 in row 8, which also are the only places for 4 in that row, so it's a hidden pair on 2 & 4. That restricts the 7 into a helpful domino and there's only one place for 7 to go in box 2. That was how I broke into the puzzle.

[@igoretski]

@@FirstLast-gw5mg Wow. Impressive. That quickly solves all the 7's in the puzzle. Then you also find the 2 in column 4 must be in box 8, where the 24 pair is and thus get the 4 in box 7, like Simon.

[@nguyenn7729]

@@FirstLast-gw5mg ye I solved it using the 2's and 7's swordfish which give a 156 triple in row 8 c4,5,7

[@Fabroskii]

At 13 minutes I was questioning whether this was part 1 of a multi-part series lol Well done Simon !

[@markme3259]

Fast forwarded

[@jhuggett1938]

what does lol mean

[@acestar01]

@@jhuggett1938 Laugh Out Loud

[@Oss-6342]

@@jhuggett1938laugh out loud

[@jhuggett1938]

@@Oss-6342 but what does that mean?

[@guanyin19]

This was definitely a puzzle to highlight the importance of hidden pairs. There are also a couple of swordfishes on 2's and 7's in rows and columns 1,5, and 9. However, the puzzle is more quickly solvable by spotting and using the hidden pairs instead.

[@SandyS.787]

There is instruction in this video. For a SLOW player such as myself, the thinking-out-loud really helps. Definitely will watch the beginning of this tutorial again.

[@dvkprod]

I love the bassy sound of your keyboard, it really adds to the incredibly emotionally soothing experience of your videos, which in some weird way cohabitates with and even enchances the intellectual side of the subject at hand.

[@HerveAttia]

video starts at 4:52

[@TheGuitarded1]

Thank you! Guy kept rambling on like it was never going to happen.

[@guzideerden6523]

Thank you

[@Swimming_with_Josh]

Boi the video starts at 0:00

[@rweisele]

Finding the hidden pairs has been a key that I discovered some time back, and though I do it a little differently, it is still the key that unlocks some of these classic puzzles. Without using the technique of finding 'hidden pair' you are really in the dark trying to solve some of these!! Thanks, Simon, for reassuring me that I am a true Sudoku solver, and I love watching you do the really tough 1, 2 and 3 digit starters!!

[@RasperHelpdesk]

Nice to have a puzzle that doesn't require solving a system of equations to start ;)

[@sgarcata]

no kidding... I've put doing Calculus proofs behind me although I have to say I loved doing them in my 20's.

[@robertparker9896]

That's what I like about sudoku - one can construct a puzzle with any set of 9 symbols; no numbers at all, so equations are out. It comes down to pattern recognition ... and now 'hidden pairs/triplets' gets added to my HARD problem toolbox.

[@frselsig]

I think there's a swordfish on 2s at 8:30 - r4c1, r8c1, r3c5, r8c5, r3c9 and r4c9. Not actually tried to see if it makes any difference, but it looks like its there.

[@yura_riabov]

Also spotted that

[@bobjonson3528]

There's swordfishes on 2s and 7s in columns 1,5 and 9 and in rows 1,5 and 9. If you look closely, you can spot that all digits in the rows and columns 1,5,9 align. After that I looked to see which digits don't appear as givens in those rows and columns, and those digits where 2 and 7. Than I looked to see where would those digits be in those rows and columns and realized that there are 4 swordfishes in total, all of them being either a swordfish on 2s or on 7s.

[@_mnejing]

@@bobjonson3528 Overcomplicated, there's a simple 2/7 pair in C5 that decimates the whole thing right from the start.

[@Buizerd88]

there is also a swordfish on 7s, combine those and you get the hidden pair 2/7s. with that, its doable.. I assume there is also something going on with the 3s, but as far as I could tell its not a swordfish

[@snjyjn]

When I attempted it (without watching the video), I pretty much pencil marked the whole grid, and then found the swordfish. After that it was quite easy to solve. The difficult part was spotting this swordfish.

[@ronaldkoh5281]

Wow, I am totally enlightened. Brilliant. Pure logic without all the clustered numbering. Thank you very much.

[@stratolightdude]

whenever I feel sad or down ...., i just have to watch Simon solve a puzzle ..., ANY puzzle. :-) Thanks so much for the great tips from this one. VERY.USEFUL!

[@bexwiedasbier]

Really love when Simon gets out the guitar

[@grenvillephillips6998]

I loved that one. It was like seeing a lock being picked.

[@rheffner3]

I have no idea how you do these puzzles no matter how many times I watch them. But I still watch them.

[@david203]

Most of the basic solving rules used here are easy to derive from the definition of sudoku. And the more complex rules involving patterns, that are not easy to derive, weren't even needed here once the first few numbers were found. The most difficult puzzles that require recursive trials to find every number cannot be solved by a small set of simple rules at all. I'm saying this as though it is fact when it is just my opinion, so can anyone please correct or confirm this hypothesis?

[@victorducedre5776]

8:56 to solve. This channel is definitely helping my out-of--the-box (in-the-box?) thinking and observation. Eight months ago I couldn't tell you what a swordfish was, and now I lucked into two of them. Edit: Swordfish on 2s and 7s revealed the hidden 27 pair, which led to the 4 in r8c1, which resolved both swordfishes.

[@gracievallee2551]

I am an amateur with sudoku who has started to do some sometimes puzzles for the challenge and I was very excited to hear you say that you only write notes in boxes if there are only two possibilities because I also do that! maybe everyone does it but I was proud of myself

[@rayling23]

It was the same for me too! I felt like a genius for a little while.

[@robertparker9896]

You can also sometimes use triplets (3 boxes row/column with same 3 digits only). it clears all remaining boxes any member of the triplet in that row/column.

[@jadenshah]

Sweet home alabama was the last thing I expected to hear during this into

[@RootballJohnson]

And from a Brit who says, “Bobbins!”

[@GevinShaw]

Very happy I noticed those 37 and 27 pairs, not by seeing the pattern in the givens but by methodically working across the rows and down the columns. Definitely made the puzzle manageable. You know, as long as you don't screw up unrolling a pair four moves from the end.

[@Luna_Aberra]

After 8 minutes of starring at this time I just gave up and watched more tips on how to solving Sudoku. I am still greenie in learn. And still many things I don't understand but thanks CTC for get me hooked. I love Sudoku now more than ever before and I think it's even my favorite kind of puzzle to do

[@SallyJaneRobson]

I love Sudoku. My brother sent me a link to your site. It’s such a pleasure listening to your enjoyment unfolding the puzzle. I like to search for the patterns of three corner numbers throughout and their overlap with other three corner numbers and then work from as to what is excluded…

[@andrewnelson2525]

My first digit in the grid was at 27 minutes (the 4 of course). Solved by 33:50. Quite satisfying how it quickly unwinds after the beastly break-in. I was amazingly sparing with pencil marks (for me). Following the influence of this channel I limited myself to two marks per box or cell except for column one which I filled in all the possibilities in an act of desperation before I finally spotted the 27 hidden pair. Loved it.

[@Oszilgath]

I didn´t recognize the pattern, but with "a few" more pencil marks, i was able to spot the two pairs and the 4 in c1. And at this point it got easy. But I´m still amazed by your skill solving this in about 15 minutes and explaining it simultanously. It took me about 38 minutes to solve it.

[@carymclean3349]

Thank you for teaching us to find hidden pairs! Although still confused about how you came up with the 5-9 pair in the upper left square. Will ponder this for quite a while…..

[@elevendarter112]

I stopped the video at about 1:10, drew my own sudoku, filled in all possible numbers and then gave up... There were 7 cells with only two numbers in them and I thought that it might be the key...then I was wondering how you would go on with that and watched the rest of the video. Wow! What a briliant solution.

[@pamrogers5979]

same :)

[@Frie_Jemi]

You ran out of gas on the 4s while you clearly still had to half a tank...

[@christopherdavies7213]

Who else was shouting at the screen at that point?

[@onedwinone]

@@christopherdavies7213 I laboured through the start, notes everywhere ,had to watch to get the hidden pairs and then bamm 15.46 he missed the fours and I was away , so pleased with myself but without Simons great skills I would have had to give up. Not all my own work but still a good feeling , thank you.

[@SamCoca]

@@christopherdavies7213 Yes, the 4’s should have kept moving. Lol.

[@namelessminionveinreaver3763]

I wanted to try it myself before watching, and I didn't spot the hidden pairs. I Goodliffe'd and marked every cell in the grid before I started to catch on. That ended up being quite enjoyable. Every digit did a lot of work on other boxes, sort of like I was being lead around the grid.

[@sergeyvoytsekhovskiy8373]

im sorry, what does Goodliffe-ing mean?

[@namelessminionveinreaver3763]

@@sergeyvoytsekhovskiy8373 Mark Goodliffe, the other host of the channel, has a tendency to go overboard with the pencil marks, putting them in more than 2 corners of a box or putting more than 4 in a center, the standard method.

[@sergeyvoytsekhovskiy8373]

@@namelessminionveinreaver3763 oh, i see, thank you!

[@kristinbyers6275]

I saw that pattern and the almost symmetry with those numbers but could not figure out what it meant. Thanks for a great demonstration! I learn so much here.

[@BryanLeeWilliams]

I am just looking at this puzzle before I start and noticing the beauty of it. In the left 3 boxes are the numbers 1 to 9 once each, the in top 3 boxes are the numbers 1 to 8 once each, in the right 3 boxes are the numbers 1 to 9 once each, in the 3 middle horizontal boxes are the numbers 1 to 9 once each.

[@roland1837]

I found the swordfish on rows 1,5,9 with 2's because you have taught me to look for them... thanks Simon!

[@TafferBoyElvis]

I imagine some people wouldn't watch a video like this, but it was quite engaging. I saw the 2s and 4s fall into place in my mind while I was watching you talk about the other numbers.

[@charlottegracedel9686]

I have just recently begun playing hard level sudoku and have played this puzzle twice while watching your video. I must say it was fun!! You did an excellent job explaining how to solve it.

[@bananacat9139]

I've solved more sudokus than I've done in my entire life. You inspired me back to play with sudokus and I love it so much. Thank you. And It's very addictive.

[@finleyherrmann4048]

Haha the casually roasting Mark for probs bifurcation made my day.

[@karadana11]

First time commenting on your videos, after almost a year of isolation I managed to solve in 4.15 and its all thanks to you guys.Thanks for all the fun.

[@_-_-Sipita-_-_]

Steps: 1.Look at the 2 and 7's pencilmarks, with the pencilmark loop logic you can cancel some cells so they are not 2 or 7's. 2.With the positions of 2 and 7's you will notice that they always occupy R3C5 and R8C5, so its a 27 pair. 3. Solve the 4. 4.Solve the rest with simple sudoku logic.

[@_mnejing]

Absolutely the simplest way to do this puzzle. The 2/7 pair jumped out at me, and the puzzle literally fell apart in a matter of 5 minutes. It took me 2 attempts (first didn't see the 2/7), the first attempt ate up around 15ish minutes of my time, but restarted, found the 2/7 quick, and was done in under 7 mins. It's a weird one. It's fun reading the comments about using swordfishes and slot machines and all sorts of random stuff, when it's whole linchpin is a 2/7 pair.

[@fherozzz1]

@@_mnejing can u pls explain what a hidden pair is and how to spot it/them. A rookie sudoku player enquiry!

[@TeoElryns]

I've finished it in 20:56, i consider myself amateur trying to solve hard sudokus recently, so i consider this as an achievement :D

[@TheLukeskywalker2]

I am so proud of myself for noticing the 2 swordfish on columns 1, 5, and 9 without Simon noticing it.

[@MiguelGarcia-to6cs]

How do they work?

[@TheLukeskywalker2]

@@MiguelGarcia-to6cs The Tatooine Sunset video that Simon explains them well.

[@TheLukeskywalker2]

kzbin.info/www/bejne/ioKTnaalact9sM0

[@Buizerd88]

just 1 small step further and you would have cracked the puzzle, there is also swordfish on the 7s, and combine them and you get the hidden 2/7 pair

[@ericcrowell9493]

@@Buizerd88 That was how I solved it. I was genuinely surprised that Simon didn't spot the swordfishes...

Really liked it! At first glance it seems like it just wants to annoy you but as soon as you get behind the hidden pairs, it opens up completely :) Thanks!

[@Grikkez]

Alternative solution path: Use slot machines on 2s and 7s. This gives a 156-triple in row 8. The rest is now easy.

[@crazypomp927]

I did the slot machine on 2s and 7s but don't see how that leads to 156 triple in row 8. Edit: I found the triple but it's not as simple as just doing the slot machines on 2s and 7s first. The slot machines don't give you any digits directly but allow you to rule out some 2s and 7s. This leaves only two positions for 2s in row 8, and combined with the given 4s in columns 3 and 4, you get a 2-4 pair in row 8. This eliminates a 7 from r8c5 and gives a 7 in r9c4, which unwinds all the 7s in the grid and leaves a 156 triple in row 8.

[@Qazqi]

@@crazypomp927 The triple appears when you list per-cell candidates along the row. 3 cells can no longer be 2 or 7 and 156 are the only possibilities left.

[@Grikkez]

@@BremSterPuzzles Yes, I realize that using swordfishes would've been easier than using slot machines. I watched a video with slot machines earlier today and realized that all the offset clues were positioned perfectly for slot machines. I was so focused on slot machines that I didn't notice the sword fish patterns which emerged. (Still, even though the sword fish patterns are probably easier to spot, the slot machine patterns more immediately resolves all the 2s and 7s in a swoop after noticing the interactions in row 8.)

[@Stratelier]

Also found this solution path, practically by accident (I did purposely check all digits for swordfish, finding only 2's and 7's, then noticed the 156 set almost by coincidence).

[@nigelm5777]

As we might expect sudokuwiki rates this as gentle/easy because the hidden pairs are found on the first step, followed by nothing more difficult than hidden singles. Chalk this one up to the computer? Fascinating!

[@weskingston264]

I feel kind of proud about this one! (24:44). I cracked this pretty easily, but ONLY because I knew to look for shenanigans (because this is a puzzle on CTC, after all)! I was channeling my inner Simon in the beginning systematically making my pencil marks, and noticed that I couldn't fill in many pencil marks constraining to just two locations, but there were many locked to three positions, so I figured I'd return to those once I'd done what I could. Then my spidey senses were tingling saying 'look at the 2s and 7s'. Once I realized there were only two possible configurations of the 2s and 7s (because of how they were locked in column 5), I channeled my inner Mark and bifurcated. My first go was looking promising, but was ultimately a bust, so I reset and sailed through the puzzle after that. I'm curious to see if there's a logical way to figure out which path was correct! Watching the video now!

[@Piatato]

Very proud with myself to have managed this in just under 30 minutes. I found it a very rewarding puzzle!

[@dvdspndl]

Nice one. I did it in like 15 minutes by finding the exact same 27 hidden pair in col5 and then the 4 etc. What made it a easier for me is something that you call a slot-machine but in fact there's a clear and simple pattern to it - it's sort of a generalization of an empty rectangle. I applied it to 2s and 7s, and then it was very easy to follow.

[@readersrock101]

i watched this video because it was a short video that would help me relax before going to sleep, but this actually gave me some tips to help me with a hard puzzle ive been struggling with for days!! i can’t wait to revisit it tomorrow and use what i learned

[@Zift_Ylrhavic_Resfear]

I pencil marked every time there was 3 options in a box instead of 2 like you, and when i got to 8 i was getting a lot of these and i saw a lot of patterns like in the sudoku with 10 hidden swordfishes so i went to hunt for swordfishes. Found one on the 2 and 7, which got me the 27 pair you so easily spotted, which removed the pencil mark of 4 in box 8, unlocking the rest of the puzzle.

[@SamCoca]

Great tip! I’m always going to look for hidden pairs from now on when I get stuck. Thank you for the great lesson.

[@michaelblower679]

Really enjoyed your video on this classic sudoku puzzle. You video helped me learn a couple of new solving techniques, that I had not yet added to my skill set. Thank You !

[@Anrui_Ishi]

I found a swordfish on 2s at the beginning... I got so excited that I spotted it that I promptly forgot what I was supposed to do with it,..... Facepalm

[@joekerr3638]

“For Bifurcation I give him no credit. “ What about partial credit?

[@jbftcmof]

I think they should split the credit.

[@tabularasa0606]

Nope, 0 points for Marc. All 10 go to Simon!

[@ordinaryhuman5645]

No credit implies no partial credit.

[@lsmart]

Well, you either consider it cheating or not. If it's cheating, you get a zero.

[@rohanmathew7577]

Whats a bifurcation?

[@chessvoices]

Most enjoyable. The 8 pair was in the top right square but you missed it early on. I feel I'm almost drowning keeping up with you. It's very impressive how fast you work.

[@pritikshettry2261]

What a way to solve this sudoku puzzle. Simply awe struck. Hats off.

[@BrianBernardEngineering]

Can confirm, it's an absolute beast without finding the hidden pairs

[@rblossey]

yep, I needed a finned jellyfish on 8s-eventually reducing to a swordfish (in the other direction)-to solve it without the hidden pair!

[@KyleWitten]

@@rblossey I had to do complete notation to solve it on my own, but a naked quad in column 5 unwound the whole thing.

[@rblossey]

@@KyleWitten this is one of those puzzled that deserves a second solve! I will try it again and look for that ;) I was a hairs breadth away from writing in all the candidates too! had I been doing it on paper--without that convenient coloring feature--i probaby would have!

[@LK-3000]

I started out watching you solve it and then I just went on my own. I do like seeing your strategies, though. They are so different than my own and it's a beautiful learning experience.

[@pardox28]

50:09 for me. I used the slot machine method to get where the 2s and 7s were in the grid. Got stuck for a few minutes & then noticed in column 5 that there was a hidden pair of 2s & 7s where Simon spotted them much, much earlier than I did. From there the 4 unlocked the 2s & 7s & it was easy from there on out. Super fun Classic mainly because the techniques that this channel has taught me are finally becoming ingrained in my solving. So thanks so much, Simon!

[@mepiffi]

Finished at 42 minutes, finally I felt that the weeks of watching the channel and working with the apps payed off! Swordfishes on 2s and 7s were my break-in. Thank you Mark and Simon for strengthening my skills!

[@HibachiQueens]

Are you able to train me for two hours in sudoku?

[@qivarebil2149]

I found the 4 in column 7, row 6 first. Relatively simple from there. My method is focusing on the numbers from 3 to 7 only. I don't like doing the pencil marks. Makes me feel unfocused. I just need to have all cells in the count all the time. While memorizing the known numbers, I delete them from my sight - just staring and staring at the sheet until they disappear, and then it's easier to imagine where the missing 3s to 7s go. I guess it's just a concentration exercise. Focus, focus, focus - and then suddenly, light! 2 years since I had to give up a 9 cell. But when they come like this one, they always leave me in physical pain, though. Sometimes for hours! I could never solve this one, while at the same time explaining it on video. I need to be extremely quiet, and don't tolerate any noises around me, But You did very well, Simon!

[@iwarx1]

Spent 30 mins with no progress. For kinda reason thought this will be possible by looking at the video length :D

[@Zasqdddas]

I usually go by difficulty being proportional to video length. I went through all of the numbers, and was only able to place a couple of pairs. This puzzle wrecked me. I gave up on a logical solve, so I bifurcated by assuming a "2" in the top right of box 6, and wound up with a contradiction filling in 7s. Once I had placed a single digit correctly, it was a straightforward puzzle.

[@SamAshworth91]

I did the same, I tend to use around 25 mins as my break point, but got nowhere with this.

[@kaybrown8885]

thank goodness for this video. I couldn't find the second hidden pair and caved to watch the video to that point and get going. Loved it, thank you!

[@sdrawkcab190]

I wasn't able to spot the hidden pairs like you did, however I used the slot machine technique to eliminate a 7 and I think a 4 in row 8 which gave me a 156 triple allowing me to place the 7 in box 9 as my first digit which similarly cracked the puzzle for me.

[@psychopietsuzuki]

I really love the way you show your train off thought. I learn the best by watching you.

[@Kelters]

32:46 -- There's a fine line between logical tracing and bifurcation. However, I think my solve was logical. After studying it for a while it became clear I would have to work with pairs (or something like that) From a 27 pair in c5 I got to a solve. Difficult until you get a couple of digits, then the rest just follows like any Sudoku with that many digits already given on the board. -- (edit) now having watched Simon get that first 4 by a much better path from the 27, I see I could have been more logical after all! However, not disappointed either. And - Well done Simon!

[@Arkanelancer]

This was my first time actually completing a puzzle that you've done a video on. I solved it before watching, it took me 27:43 and I started out with a guess made after making some pencil marks. Some of that was because I'm not used to the controls, but most of it was just me struggling to place that first number. It does make me feel better that you also took a while to put the first number in, but watching your logic for this class sudoku was really compelling!

[@lct9elliot66]

guessing doesn't use your brain which is the whole point surely? anyway - good guess - mine are usually bad :(

[@johnpinchard6261]

I take a screen shot of the starting puzzle and load into Soduku+. Having pencil marked all two digits per box I then allowed myself to pencil mark three digits. The puzzle then seemed to solve easily (12 minutes) without any clever techniques. I am far from an expert so was pleased with the result.

[@Xhopp3r]

I have a classic sudoku app on my phone that I play almost daily. I always play on extreme. When I solve a puzzle in 8 minutes and I see I am only 30% above others, and then I see this video in which a very smart man solves the puzzle in roughly the same time, then I know the other 70% have cheated. Great job at solving this puzzle.

[@SoRTs6233]

That was amazing! Oncce you found that 4 (just after 16mins) The rest of the puzzle just opened up! Those hidden pairs are tricky. Thanks for a great solution.

[@johnkey350]

Ever since that video when Simon marked cells eliminated by swordfishes by a center pencil mark, swordfishes have become so much easier to use once they're found. Def recommend. Took me 25:06 with a distraction in the middle.

[@skimeup]

Fascinating to see him finding the hidden pairs. I noticed all the offsets but didn't know what to do with them. However, I found two swordfishes on 2 and it unrolled from there.

[@junebug406]

I was able to get the hidden 27 pair by marking out the possible 2s and 7s on the grid, but never noticed this solved a 4. After watching the video up to that point, I immediately hopped back in the puzzle and it just collapses down after that. Great video, I love when I get to see something after missing it for so long, even if a much smarter person points it out to me.

[@negar1368]

I'm so proud of myself for solving this! Thank you CTC channel!

[@roccoberetti7066]

you're possibly the first world puzzle solver's champion/ sudoku's champion who just came out and said 🤠🎸

[@danielrhymer1762]

13:07 for me. Used colours to work out the possible positions for the 2’s and 7’s and realised there was a 27 pair n column 5. From that I got the 4 in box 7 which solved the 2’s and the rest dropped out easily.

[@kaiwienbeck8598]

so did i, not hanging around what could have been there too, if you find such a pair also the solution must to be find there! because once the sudoku must have been constructed as a puzzle!

[@QemeH]

Bloody Nora, I had to use half a shedload of colours to get my head around the opening - 51:40 [Edit: Watching the video, I'm once again reminded how much better Simon is at solving these than I am. He spotted the hidden 2/7 pair in what felt like seconds - I had to color the whole grid with all the options for 2's and 7's to come to that conclusion. But I have a small consolation price: I did spot the effect on 4's in the bottom three rows faster than Simon did. That's something, innit?] [[Edit 2: In case somebody is curious, because I know that some people are more visual types, here is how I managed to do it: First you realize that Boxes 4 and 6 have two possible placements for both the 2 and the 7. Then you pick colors for the options (e.g. green/red for the two options for 2 and blue/purple for the two options for 7) and run them around the grid. Every color option "finishes" the grid, so you'll have 6 squares of each color - with one little twist: two squares (the ones that will become the 27 pair later) have two colors at the same time - one is a 2 option and one a 7 option. This means, both of these colors can't be true at the same time; ruling out two of the four possible color pairings. You are left with the question which of these pairs is true. This is not resolvable at this stage - but because Boxes 2 and 8 have colors from two _different_ pairings in them, the double-colored squares absolutely _have_ to be part of the working pairing - which means they have to be 2 or 7. And that's how you get the 2/7 hidden pair...]]

[@MystearicalX]

Another amazing cascade! I needed help to find that first 4, hidden pairs are brilliant, but once that appeared it was very straight-forward. The whole thing just fell into place. Timer says 35 minutes but a good 12 of that was watching the video to get an idea of what I needed to do lol.

[@StephanSpelde]

I was able to solve it in half an hour by using the slotmachine trick on all of the offset digits. That left a couple of empty cells which could therefor only be 1,5,9. These, in combinations with cells that could only have 1 of the other digits after they were slotmachined, made quite a few quadruples, which made the puzzle fall apart quite easily. I'm happy to have a learned your scanning trick though!

[@HalfBakedLunatic]

Thanks for the explanation of what 'classic' Sudoku's you like to feature ... I have run across some computer generated puzzles that seem downright impossible - and when I use Andrew Stuart's "solver", it has to use the crazy extreme strategies with "grouped X-Cycles" and "Cell forcing chains". I've been curious how you would approach some of these puzzles.

[@claudiagreen9277]

why is no one pointing out that his intro riff is "sweet home alabama" this is the best thing i've seen all day

[@bighouse1695]

Hidden pairs and the extra numbers it eliminated were the whole 🔑. Brilliant job!

[@alivegmusic9761]

Hi. I just came across this Sudoku . I only saw the first few frames and decided to solve it manually with paper and pencil without seeing the rest of the video. Not so challenging. I had more difficult grids. Done in about 15 minutes (with few long interruptions from wife and children). I didn't see the rest of the video as my solution is correct. I have been playing sudoku on my tablet since the first day it was available and I always solve the pro or difficult level. It takes me between 4 and 10 minutes depending on its difficulty and how quickly I press on the touch screen. Over the years I have developed on my own multiple techniques to crack it and I never saw anything on Sudoku online or tried it manually until now.

[@gordonflash8976]

Hidden pairs is new to me and greatful for the lesson, thankyou. Question: Is it always nessary that when you find a pair, that the otherwise third or fourth possibility for that square is therefore impossible for that square?

[@hollyberry4647]

Never knew there were names for some of the patterns I can see in sudoku puzzles. Definitely going to watch more videos!

[@IvesBon]

Very nice, thank you! How are you forcing two numbers in the middle of a cell?

[@imaginarycastle]

Very nice puzzle! After reading some of the comments, I have gone back to try to spot the different suggested paths, like practising finding swordfish patterns. There is so many interesting things going on in this one grid!

[@ib9rt]

I haven't watched your solve yet, but for me the key was a couple of hidden pairs, then two overlapping swordfishes, then Snyder notation did the rest.

[@Jopal2222]

I've been watching too much CTC, as I found this relatively easy! (was expecting another Tatooine Sunset). My first solve which is faster than Simon's video.

[@mendelsonja]

Not to downplay your achievement too much but, aside from not starting until about 5 minutes in (and then finished his solve a minute before the end of the video), I believe this puzzle is the most I've ever seen Simon explain what he's doing.

[@matejailisin3194]

I'm so proud of myself for getting this one just like Simon did (tho it took me 36 minutes). If not for this channel, I wouldn't even know where to start. Thanks guys, you are amazing!

[@hilcovanbreeschoten720]

44 minutes. I found the pattern of possibilities on 2s and 7s very limiting, with a maximum of three possibilities per box. Also noticing how they were arranged such that the boxes are affected in a cyclic manner (for example placing the 2 in box 1 forces the 2 in box 3, forcing the 2 in box 6, forcing the 2 in box 4, forcing the 2 in box 1). Then I started to spot any contradictions (you could explain that as light bifurcation), and I found I could reduce the possibilities for 2s and 7s in each box to only two options. For every box that had three options, those options are arranged in an L-shape, and every time the corner of the L-shape could be eliminated. After this, i started noting all cells with only two possibilities and then especially paying attention to boxes, rows and columns where 2s and 7s were eliminating. Then I found a 156 triple in row 8, giving a 7 in r8c9 and that basically cracked the puzzle.

[@tinkledeath9185]

I DID IT!!!!!!!!!!!!!! In just over twice Simon’s time!!!!!!!!!! I’ve never been so close to his solve time before!!!!!!

[@iamtedg]

What do you recommend for a Sudokus app that allows you to insert different types of pencil marks....? Thanks

[@SmartHobbies]

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.