The Best Sudoku Of All-Time?

[@RandomBurfness]

Something you didn't notice about this puzzle is the rotational counterparts are the pairs that add up to 10. You have 1 + 9 = 10, 2 + 8 = 10, 3 + 7 = 10, and 4 + 6 = 10. No wonder there was a lack of 5's in the starting grid, those only pair up with themselves to make 10!

[@Wecoc1]

The numbers could be swapped and you would still have a valid solution, that 10 sum property was probably made just to make it a bit easier to remember the correct pairs.

[@PeterJavi]

@@Wecoc1 Given the 1-9 property of sudokus, it's quite natural to pair numbers that way, especially if you want that extra layer of symmetry.

[@Chroniknight]

That's cool! I didn't notice that

[@sunriselg]

The best part for me about that is the way I do notation: I divide each cell into a 3x3 grid and colour in everything it can't be. That way even the numbers are rotationally symmetrical and so is the solution of this puzzle.

[@JohnRandomness105]

There was a more complicated 90-deg rotational symmetry. Rotate 1-2-9-8 and back to 1. Similar for 3-4-7-6.

[@andreww4473]

Couldn't have done that in a million years. I'm astounded at how you solved it.

[@sunriselg]

About Gurth's symmetrical placement: If the start is symmetrical, the solution must either be symmetrical or ambiguous: Suppose there was a solution that isn't symmetrical, then rotating that solution by 180 degrees and transforming the numbers according to the symmetry would also be a solution to the same initial state.

[@asmodeojung]

That's a nice and easy to understand explanation.

[@yichen6313]

Interesting. So it's essentially invoking uniqueness.

[@Pyromonkey83]

Absolutely breathtaking. This is one of those puzzles where I wish I had more friends interested in Sudoku, because this is just immensely satisfying to solve. It is 100% buildup of compounding logic to an absolutely stellar collapse. I did not know about the Gurth's placement rule, so the 5 in the center was actually the last digit that I placed, but it took me nearly a full hour to get there. I spotted the X Wings rather quickly, and loved going around the grid with them, but it wasn't until much later that I realized how profound of an effect those digits had on the middle edge pieces to give an astonishing hidden quintuple, followed by the hidden singles in the inside corners of the middle edge boxes. This is, without a doubt, the best puzzle ever featured on this channel, and I absolutely love it.

[@AWildBard]

I was wondering if it could be solved without knowing the 5 would be in the center, because I wouldn't be able to recognize that.

[@Desslosh]

I spent about one hour filling this sudoku with notations, only being able to place the 5 in the center. Only after a long time it dawned upon me one of the first digits you placed, and then the puzzle solved itself. Completely amazing.

[@04LightningFan]

Simon, finding that 3467 quadruple using the x wings was absolutely brilliant.

[@eternalblasphemy6526]

Honestly, all you need is to find a swordfish on 3s and x-wing on 4s to break the puzzle. Funny enough, I tried to solve it a year ago using symmetry and got stuck (thankfully, was able to solve it the stadard way).

[@cyandinomashups]

I've heard of sevens.

[@buzzly108]

I understood some of those numbers

[@phs125]

British humour never fails to let me know I have asthma.

[@NelielSugiura]

Once I saw it is just a pinwheel rotational symmetry, I applied that theorem from another video of yours and knocked out the puzzle in about fifteen minutes. This would have been a great way to introduce that theorem, too, and show that it applies not only to two directions (like a mirror or 180), but also to four (90 degrees). I feel you touched on this at the start with your mention of the "animal" shape being rotated around, but you had not noticed all the numbers rotate, too. It would have made it way faster and is a lot more creative/clever when you see that!

[@KJGrenadier]

You mind linking the video that has them using the pinwheel rotational symmetry? I would love to learn about it. No worries if you cannot; it may be hard to find (unless it is in the title?).

[@ChessRabbitt]

I would like to thank you all for this channel. Six months ago I would not be able to solve this, or any hard puzzle, at all, let along in less 30 mins. Thanks you for making me a better Sudoku solver.

[@abubakardouglas8268]

It totally stumped me. I saw the symmetry but had no idea what to do with it. Great puzzle

[@N8ive49er]

Brilliant logic with this solve. I attempted this puzzle for a little over an hour and couldn't do it. I then allowed myself the benefit of using the '3647' x wings you discovered and still couldn't do it.

[@DamianFloresRF]

I'm impressed by how quickly you solved it. I did it in about three hours. It took me a lot longer to be absolutely sure that it was ok to assume that I had to put a 5 in the middle despite not being able to prove it with common sudoku logic. After that, I solved it in a very different order. There are several steps you made that I missed, so my method was messy, but entertaining: I made a "wheel" with 2, 1, 8 and 9 and put them in the middle quadrant. I tried the three possible rotations (the fourth was blocked), looking for inconsistencies. Two failed. The third was the charm. Even if I had got it right in the first one, I would have later tried the others to check.

[@MrEvenStranger]

13:48 - I think I lucked into it. Once the fives fell in place I could compare columns, rows and squares to eliminate numbers and place digits.

[@draconicdusk5911]

So, I spotted something. We can use uniqueness to crack this puzzle wide open. in the 5th box you have: 128 in square 2, 129 in square 4, 189 in square 6 and 289 in square 8. Now the thing is, what I spotted was that we would most likely have to solve the puzzle by placing any number that isn't a 5. If we were to assume that square 4 and 6 of box 5 were a 19 pair, we would hit a problem. The puzzle would have 2 solutions, because the 19 would be semetrical either way. Thus I ruled out the 19 from square 4 and 6 in box 5 leaving a 2 in square 4 and an 8 in sqaure 6, this left a 1 in sqaure 2 and a 9 in square 8. from there, the puzzle is easy. Took me 4 minutes after the Gurth's symetry was mentioned.

[@timdunkley9173]

Remarkable puzzle. The symmetry aspect actually being a red herring made it even more impressive. Standard corner and centre notation on its own reveals the four X wings. Then the hidden quadruple is pure genius.

[@notavan17]

Very interesting! Once I finished Snyder notation, found pairs in rows and columns 2 and 7. Then looked at 4s and followed a logic chain that placed a 4 in r3c1. Then the rest pretty much fell apart. Took 15:17 for me. It's cool watching your methods after I finished my solve.

[@Djsrox96]

Did the same thing and got it in 16:17

[@pimo01]

I am positively thrilled at the moment, it usually takes me more than a solid hour to crack the sudokus posted here but today I was just past the 30' mark when I discovered the symetrical solution. The thing is after that I didn't need any x-wing strategies because after placing the initial central 5 I noticed that, 8 and 2s as well as 9 and 1s were positionned in the same manners throughout the grid, one obliquely to the other and I dive into that and started placing the 8,2,1,9 that I could using that visual way of placement, which has no sudoku logic to it I have to say, it then took me another 15 minutes with traditional sudoku technique then to finish, really marveling at the genius behind this grid with each added digit. I'm so proud of myself there, I'mnot usually the boasting type, but really glad all the same. Thanks a lot for posting that wonderful game.

[@jakewhitttyyy]

My time was 22:41 by some amount of sheer dumb luck; but everytime it led to a new epiphany of the puzzles mechanics. After cracking the quadruple, I was smiling the whole time. Brilliant puzzle!

[@jrpstonecarver]

Woah. First time I have ever solved one of these on the first try, and without the video. 28:33. And I didn't use the X-wing technique. Great puzzle!

[@Augmentfluup]

I'm sure this has been mentioned before, but please, don't spoil the solve in the thumbnail. For example this video spoils an X-wing

[@shane8037]

At least you don't know what the number is for this one. Sometimes half the board is filled in on the thumbnail!

[@soundcrank6214]

@@shane8037thumbnails are tiny, stop studying them so intensely

[@sunriselg]

I did not pay attention to the thumbnail, but your comment spoiled it for me. I think I would not have been able to solve it without that hint.

[@KuyashiiPlays]

@@sunriselg dont read the comments on a puzzle before solving it!

[@brendabalzan1994]

I solved it without realizing there was X Wings. I saw something on the thumbnail but I still am not sure how to do them.

[@stuartw969]

Unbelievable! Congratulations! You kept calm and mastered the most difficult of puzzles.

[@Penguincw2]

Anyone here after Simon mentioning it in today's vid?

[@stereomike75]

What's the first thing that jumps out to you watching this vid? Simon's voice! It's like listening to his brother, it's so weird.

[@Penguincw2]

@@stereomike75 Definitely the change in setup: his camera is further away and he sounds different.

[@simonplanting5948]

Yes, hadn’t seen this one before... relatively new to this great channel...

[@nicksm7980]

His haircut is ok though.

[@awilliams1701]

I meant to, but I didn't have time and then I forgot so here I am 5 days later. lol

[@jimbobago]

An impressive piece of work from both the creating and solving aspects.

[@lawrencekallal6640]

Quite an amazing and unique puzzle. With a lot of numbers restricted to a couple of squares, this puzzle seemed like it was made for a forcing test solution. There are quite a few numbers that have forcing chains to follow around the board. Starting at 6:30 (need to mark in some Snyder pairs) my solution involved the right side middle 3x3 block. The 8's are restricted to 2 positions in C7, and the 6 goes in R5 somewhere, but the 6 can be restricted further through some testing. The 6 in R2 can only go in 2 positions, C5,9. Putting the 6 in either of these positions eliminates the 6 from C9 in that middle block, just follow a couple 6's from the C5 position. The 6 can now only be in C7,8. Secondly, I found that no matter where I tried to put a 3 in the bottom left 3x3 block, a 3 or 2 landed in RC58, eliminating the 6 from that square. This resolved the 6 (RC57) and 8 in the right middle block, which was enough to crack the puzzle open. Edit … another way to proceed with the 3's is to notice that the 3 in C8 is restricted to R5,9. If the 3 is put in R9, following the forced 3 and 2's around lands a 2 in RC58. So the 6 is eliminated from that square by a 3 or 2.

[@Kuraudo_VII]

This one is seriously beautiful. The total spiral symmetry is amazing. I would love to see more of this kind in the future. And this is probably the first one where I solved it with close to exact number of minutes you used.

[@Pernfan1]

I understood the shapes were symmetrical but had no idea the whole puzzle was until after and I watched you solve it. So naturally I came at it like any other normal sudoku, used pencil markings to find possible locations and gradually filled in the grid as I normally would. First time I messed up somehow so I had to start over, but I made it through on the second attempt with a time of 26:46. Just a tad over your own time, I believe.

[@JqlGirl]

I found the unwinding a different way. Once I had all four xwings marked, I noticed that they forced their opposite digit into the middle, and since each middle two had to contain both an xwing number and the number forced in by the xwing, they couldn't contain any other digits. Same result, but different logic without finding the double 3467 quad itself.

[@ericl2811]

So a few things. First, this is the first puzzle from the title alone u finally decided to try it myself with your program. (I thought it would bring me to an app, which is why I've put it off this long.) And I love that it automatically brings it up without downloading anything! Thank you so much! Second, since this WAS the first puzzle I tried before watching the video I saw the multiple X wings and the symmetry but I got completely stumped and couldn't make any progress pass that! After over an hour I finally gave up and started watching the video!

[@echoes6092]

Wow, that was an amaazing solve!

[@JohnRandomness105]

2:00 The puzzle appears symmetric under 180-deg rotations and substitutions of N and 10-N. (Later) I always need a comment or phrase, to clue me into something potentially cracking the puzzle. I'd already found two X-wings, but a comment just under mine alerted me to two more X-wings. (Later still) The comment led me to search for and find not one but two 3467 quads. There was a 90-deg symmetry. And I solved the puzzle. 4:50 The symmetric placement theorem: I think there are two versions. 1st involves placement. If your placement doesn't follow the symmetry, then you've omitted possible placements. So if you place 1 into the central cell, 9 is a candidate by 180-deg rotation. Then by 90-deg rotation, 2 and 8 are also candidates. The 2nd version of the theorem is that the solution is itself symmetric under the transformations. This version assumes uniqueness, which one should probably avoid. One would rather prove the existence of a unique solution, by solving the puzzle. If the solution is unique, the central cell must be a 5, and 5s elsewhere must remain 5s under 90-degree rotations. But if the solution isn't unique, the central cell could be another digit. 9:20 "I'm sure most of you are familiar with sevens." I was reminded of a hypnotic trick where subjects are made to forget the number seven.

[@BlakeMcCringleberry]

Wow. This was recommended to me today, and a year ago I would have been completely stumped, but after watching CTC for so long, the x-wing of 6s in R2/7, C5/9 was so apparent and obvious. Once I had that in place, and R5C7's 6 was solvable, the entire puzzle just opened up. Finished in 8m06s. I'm feeling very accomplished today.

[@G.Aaron.Fisher]

After spotting the symmetry, the 5 made total sense to me and I was able to fill it in. I didn't see the X-wings at all. However, this puzzle folds quickly to bifurcation if you make good use of symmetry. Bearing symmetry in mind, there are really only 14 unknown cells in the puzzle, rather than 57. That leaves very little typical sudoku work. Kind of like a 2x2x2 Rubik's cube, it can be solved just by playing around with it a bit.

[@johnnull1375]

commenting before watching past the x-wing discovery, I needed that help to get going! there is also a quarter turn symmetry as well, 2 to 1 to 8 to 9 and 3 to 4 to 7 to 6; so any time you get one number, you actually get 4 ! simply amazing!

[@julieannmyers8714]

11:07 but spotted nothing about 3467 or rotational symmetry! I'm an inveterate plodder.

[@georgesthibaudeau1533]

This was brilliant solving. I was not alert enopugh to see those X Wings. What I did is completely different. After entering the snyder notations as you did, and spinninf my wheels for eons, I noted the particular interactions of the 3 and 7 in that rotational symetry. In box 4, we had a 9 in two positions in the lower rows of c1, with the counterpart in box 6 being the 1s in either of the upper rows of c9. Back in box 4, the 3s were either ia pair with the 9s or in r5c3; symetrically in box 6, the 7s were a pair with the 1s or in r5c7. Now when you take a good look at that, you cannot help but see that the flow of rotation requires the 3s to be a pair with the 9s in c1 and vice versa for the 7s with the 1s in c 9. This may have been somewhat instinctive, but it worked marvels, so much so that after a very painful beginning, I finished the puzzle as if it were sudoku 101.

[@paulwatson746]

My best "Hard solve" - spot the 4 way rotational symmetries, 9-2-1-8 and 3-4-7-6, get a couple more centre groupings, soon leads to , 1 in row 2 cell 6 (using bifurcation (guess)) (this took 20-25 mins) - and everything else follows. No need for X wings at all just follow the 90 degree rotations and nice doublets miraculously appear. 29 mins totals with also having to re track from an error.

[@wazzzuuupkiwi]

this was an amazing solve, it took me 54 minutes :P and I didn't know the pairs trick. what I used was filling in all 50-50's in all rows columns and squares, found 3 x-wings that way, then still had no digits to place. but 1 of the pairs linked 2 xwings, so I decided to see how many digits I could cascade if I pick one of the pair. then the same for the other option. this gave me the center 5 and nothing else until I used the x-wing property to give me 1 more 50-50 inside the top middle square, that led to a break in one of the 50-50's cascade causing me to pick the other one and fill it all in. after that so many digits were filled in that basic row/column checking solved the rest. VERY satisfying!

[@TheHutcharmy]

I just did this puzzle in the Greatest Hits book, and I think it was one of the few I got through (so far) with no mistakes which felt great! I did see the 4-6 X Wing, but not the 3-7, so I ended up getting stuck for a while until I figured out a forcing chain involving the 5-9 square in box 2. Fantastic puzzle, so glad I attempted it and recognized how the symmetry had to work early on. Really fun solve, thanks for helping me understand how the solution works!

[@sunriselg]

The first number I placed was the 5 in the middle. Then I was stuck for a long time. Found the tip about looking for X-wings in the comments and solved the rest. Overall solving time was around 35 minutes. The great thing about this symmetry is that it's also symmetric in my own notation method - I divide each cell into a 3x3 grid and colour everything it can't be. So I solved in Gimp and copy-pasted and rotated by 180° to track all symmetries.

[@CasualGraph]

The Wikipedia page on the mathematics of Sudoku has a section on automorphic sudokus and never did I expect that to be useful until you placed that 5 in the middle of the grid. Great stuff.

[@itamarolmert3549]

took me 106:49, though had I realized the Gurth theorem being applicable sooner it would have been a breeze. Absolutely the most beautifully logical sudoku I've ever seen. Magnificent!

[@MotoCat91]

Rather than spotting the 180 degree symmetry, I actually found a 90 degree pattern instead, with the same ultimate conclusion but makes a few placements a bit easier. So working counter clockwise, 1 -> 2 -> 9 -> 8 and back on itself 3 -> 6 -> 7 -> 4 and of course 5 -> 5 So when one number gets placed, instead of only showing it's opposite counterpart it also filled in the other 2 automatically. I got the original centre 5 within the first 10 mins, but then I was at 1hr20 before I spotted that 1 as the second placement. From there it all collapsed in under 3 mins. Finding that second digit was truly evil, but it's such a well made puzzle

[@richardglover314]

For years I have laboured over sudoku, invariably ending up putting all possible candidates in and then searching out those which don't belong, so to speak, like the reverse of your pencilling in method. I started with the pencilling in method and when completed all I could see and was stuck, reverted to, filling the lot in. And hey presto could see the 2 and 8 pattern which seeing as that is what I consider I was in, simply proceeded to eliminate candidates on the basis that that was the key to solving. And it was.

[@snakeyesz]

That's incredible what you found because your first number was my last to mark down this was the first time I've tired marking everything down I see and did not know what to do, then i saw just one pair and that was in column 8 236, 236,6 then I placed the 6 in and then after that I kept placing more and more numbers that didn't not line up with my pencil marks but I kept going with what I put down also at the same time doubting it and THINKING I'm eventually going to mess-up but it did not happen. This for me was beautiful and at the same time puzzling thanks Simon!

[@adnagapot]

Such a satisfying puzzle, really excellent

[@jamesyoung1022]

Once you got me looking at the symmetry, I solved it by figuring out the symmetry alone. Looked for patterns of odd and even digits. Didn't use any x-wings.

[@geraldsmith7401]

Hi: I don't know much about x wings etc. All I did was substitute a 4 in the second column above the 2 and 9. There could only be a 4 or 5, so I got lucky and picked the right one. In doing so, It took me 21 minutes and 8 seconds. Lucky me. Thanks and keep up the lessons.

[@pietndala7394]

Wow 😳, fabulous logic👏👏👏

[@gerryandlizkeogh1817]

Even after watching it solved I don't understand it! Sheer brilliance in setting and solving well done!

[@policarpo4816]

Wow. This puzzle was truly incredible and surely the best I’ve ever seen. Also, congratulations for solving this diabolical sudoku. I had my mind blown. 👏🏻🤯

[@tadperry1817]

Okay, very interesting regarding me and this video. At the time I write, I've been watching the videos for about 3 weeks only because I found them interesting, and started trying them about a week ago, because I though "I want to be able to do what Simon does.. As usual, I started it on my own and put in all the pencil marks using Snyder notation and then continuing with the intention of starting the video if/when I got stuck. I had absolutely exhausted all Snyder pencil marks and I was certain of their accuracy. I didn't know about the implications of the symmetry and I didn't have a 5 in the center. This approach had not produced a single "normal" entry. I hadn't noticed that the numbers themselves had been paired up. So I did what Simon always suggests at that point and looked for the most highly restricted squares and found the 57 and 59 pairs in row three by process of elimination. I kept going forward. In fact, I found the 56 and 25 pairs in column 8 as well as the 35 and 15 pairs in row 8. At this point, I was worried that I was making my usual logical errors and wanted to watch the video just to see if Simon was doing this the same way or had a better method. I was absolutely gob-smacked to see what he did to get all the same information! He abandoned continuing with Snyder and switched to using the symmetry in the grid!! At least I was happy to find that I hadn't made any mistakes and turned the video off when he found the last 45 and 58 pairs in column 2. At that point I stopped the video and went back to trying to solve it on my own.

[@tadperry1817]

57 and 59 in row 2.

[@ScorpioPK]

It took me almost 3 hours to solve and I was getting frustrated that I knew the middle had to be a 5 (instinct, I guess), but I couldn't prove it. After 2 hours I managed to eliminate 5 from the middle line/column of each outer cell leaving the 5 in the middle. And you just did that in the first minute because of a rule I never heard about. I guess I basically proved it :))) Then, it took me another 30 minutes to spot the quadruples (1289) and then it collapsed. I am usually no good at finding X-Wings or other techniques (I am new to sudoku), but I did find 4 X-Wings and 4 Y Wings in this puzzle, which didn't really help that much. Beautiful puzzle!

[@ManfredoStagnoGD]

Yes, that is the best sudoku of all-time! What a puzzle!

[@ScorpioPK]

First of all, I am a beginner and my theory on sudoku is 100% what I learned from your videos. I spent around 2 hours, I filled in the entire board with all possibilities (because I couldn't find anything else I could do). I have found 4 x-wings and still couldn't fill in a single digit. I gave up and decided to watch the video and see you solve it. You put the 5 there in the middle and I went back to my puzzle which fell apart in 10 minutes.... I guess theory helps sometimes.

[@WaldoHazeleger]

Fascinating puzzle! It is funny that you can solve the puzzle without x-wings if find the 3467 quadruple, and that Duncan's solver only found the quadruple after the x-wings. Also funny: If you disable x-wings in the solver, it finds the solution with 4 x-cycles. If you disable the x-cycles as well it finds the solution with 4 jellyfish'es. And if you disable the Jellyfish (and grouped x-cycle), it finds a really nice Empty Rectangle !!!

[@Zuzurp]

There is actually a 90-degree rotational symmetry (3>4>7>6 and 1>8>9>2). But so far I am failing to see if it could help solve it a bit more easily.

[@richardhenrysutterrosendo3439]

Thanks! I was looking for this in the comments, to see if more people noticed it too. Indeed, the best puzzle already presented here.

[@richardhenrysutterrosendo3439]

Also, this helps by forbidding 5 along the main diagonals (except from the central cell). But I was not able to use this fact further.

[@christiancoester2455]

Amazingly, there is not only a 180-degree rotational symmetry where x maps to 10-x, but also rotation by 90 degrees always maps the digit x to f(x) for a fixed function f (e.g. 1 always maps to 2 when rotated by 90 degrees counter-clockwise).

[@SawyerAndGretch]

Learned a lot from this video. Saw the symmetry, but did not think about the x-wings.

[@gposchman]

I went back a second time to fill in the open cells and admire the symmetry. The interaction with two digits equaling 10 was amazing. As I followed the symmetry about the grid I discovered that using the symmetry in conjunction with the number 5, I could set four numbers in the grid which slowly collapsed the entire puzzle. The completed puzzle is an incredible kaleidoscope of the number 10.

[@itsmeagain1745]

So maybe the meaning of life is not 42... It appears that 'The Hitch Hikers Guide to the Galaxy' got it wrong!

[@rabidsamfan]

I love how many different ways people approached this!

[@SamuelWebster1337]

Got this in about 20, only found 2 of the x wings I think, but regular pencil marks got it from there. Absolutely stoked, one of the most satisfying solves I've done!

[@allanlindjensen2306]

There is a stronger symmetry: Rotating 90 degrees to the left maps 1 -> 2 -> 9 ->8 -> 1 and 3 -> 6 -> 7 -> 4 -> 3, and then 5 -> 5. Is there a way to weaponize that observation?

[@yichen6313]

Wow, beautiful! I didn't use any rotational symmetry arguments since I was not sure if it's guaranteed that the initial numbers are rotationally symmetric that the final solution is also rotationally symmetric, though in this case, it turns out to be true. (Time to look up some proofs) What did it for me is the bent quadruplets in for example r8c6 + r3c6, r3c8, r3c9, which allows me to erase some pencil marks in c6. Similarly for the few other places on the board. Then some quintuplets appear in r5 and c5. Then it breaks open.

[@yichen6313]

Hmm the Gurth's argument is essentially a uniqueness argument. Not a big fan of using it...

[@kradoyen4929]

A new PB for me! 17:20 without watching the video first time I have a time below 30, can't believe it

[@r0bw00d]

I'm not nearly good enough to tackle this level of challenge. I spent 45 minutes just with the pencil marks and, although I spotted the spiral pattern, I didn't know what to do with it.

[@The_Cali_Dude_88]

Due to its rotation notice, your inner block numbers 3, 4, 6 & 7 end up at the edge of the entire puzzle corners at the end. Additive numbers surrounding the 5 end up in their respective center points on the outside s edge as if the central block of the cube just 'blew' up and a puzzle was created ✨️

[@piarittersporn]

What a wonderful trick. Now I have learnt a new lesson.

[@Blubb5000]

I managed to crack it by finding quads in row 5 and column 5, which ruled out a lot of candidates. From there on it was a breeze.

[@tessjuel]

That's an absolutely amazing puzzle, thank you for posting it! The only problem, I tried to do a regular sudoku afterwards and struggled because I kept lookign for the symmetry that wasn't there. ;-)

[@wizardsuth]

Interesting use of symmetry. I solved the puzzle before watching the video, and found the four x-wings, but it took me a while to spot the naked quint (12589) in the central column.

[@solfeinberg437]

Gurth's symmetrical theorem. The placement and the values of the starting grid are symmetrical around the 180 degree rotation. Seems like this would automatically mean the full solution would have the same symmetry. (Or there would be some symmetric ambiguity.)

[@1002l]

40:00 had to do three swordfishes then it flowed nicely

[@nibletsgo599]

This one was fun! I noticed the x-wing on the 7s. But rather than focus on the rotational deal I highlighted the remaining cells that could be 7s and found a swordfish which helped me place the 7s and crack the puzzle.

[@cindyshirey8561]

LOVE THIS ONE !

[@ericwallhagen3146]

Lovely puzzle. I got a lot of pencil marks, but completely missed the x-wings, and consequently the quadruple down C5 and R5. Ended up noticing chains with a lot of the doubles/pairs I had marked, and ended up doing a bowman's bingo to eliminate one possible option, which caused the rest to completely collapse. Happy I solved it, wish I could have seen the beauty in your solve though.

[@daveturner5305]

Fascinating! I did solve it eventually, though much more tortuously. For the 'hell of it' I then put it through Duncan's solver; which ,with the exception of the central 5, followed exactly your solution path.

[@HolyChez]

It took me forever and a lot of staring. Came back to it on and off over 3.5 hours. First 2 I was just astounded by the spiral-like symmetry and had a hunch that the middle had to be five but couldn't prove it to myself yet, so I kept looking for ways to prove it. Had the 4 x-wings highlighted and restarted penciling in numbers, but this time deciding to only pencil in only doubles and middle pencil the x-wings similar to the solve in the video. (Watching your other videos prompted me to try that.) With every available double I saw that each x-wing forced the others by way of the corner 3x3's double interactions. With that the x-wings had to be inner or outer (which is my way of saying if the '6' x-wing had the 6 closest to the center it was inner, and outer was the other way around). If I put anything other than 5 in the middle it forced inner x-wing patterns, which in turn forced the fives to be in the edge squares forcing 5 to not be in the middle square at all: my first contradiction. With 5 in the middle square it was determining that the x-wings couldn't be outer arranged through trying to put numbers in and finding the fives in those 2nd-in rows/columns pushed to the corner 3x3s and made a contradiction in the edge 3x3s: I found the same contraction occurred in the spiral-like symmetry all around. Then the puzzle filled in itself from there. Absolutely stunning.

[@BLACKATELIER]

just completed in 8min 22 while listening along, great puzzle

[@JXPLennox]

I was able to solve it without any advanced techniques, no conclusions from symmetry or x-wings. The 5 in the middle was the fifth to last field that I filled in. It took me 27:28.

[@jimjimellell]

The first hint was that there were no 5's at the start. After penciling in unmatched pairs I noticed that many contained a 5. Nearly 2 hours of crossing off conflicting pencil marks,(using no advanced techniques), I was able to write down my first digit and it was a - - - 5! After that the puzzle just solved itself. This is the only Sudoku that I have ever done that was like this. I want more!!!

[@chrisengland5523]

That's the most weird Sudoku I've ever seen. I managed to solve it before watching the video, albeit not in the time that Simon did it in. I used the symmetry and the X-wings, but then did the rest in a different way. The 4 initial X-wings eliminated digits from several squares, which led to what looked like 4 more X-wings, but in each case, one of the 4 corners was blocked (seen by another identical digit), so these 3-legged X-wings immediately gave me the pairs of digits and then the puzzle fell apart. (To be fair, I had already seen Simon's other video on Gurth's Symmetrical Placement, which gave me a big starting advantage.) Watching Simon go through the same steps and discovering the X-wings was really funny. Simon struggled with the notation at one point and used central pencil numbers to annotate the X-wings. I had an advantage here, being an electronic engineer, I am familiar with the resistor colour codes. Each digit 0 - 9 is represented by a different colour and whilst the colours available don't quite match the required colours, I was able to identify the X-wings by colouring them with the relevant resistor colour code colour. That helped a lot. It would be useful to be able to use red pencil numbers to indicate where a number is NOT possible. That would be far cleaner than listing all the other numbers and missing out the impossible ones.

[@joopjansen9102]

I was not sure about that central 5, so I decided to ignore that as a given as long as possible. With the (brilliantly found!) 3467 quad, the puzzle can be finished without that central 5. What I took from your explanation is the symmetrical bit - not as a rule, but more as a clue to find the x-wings. I had found the 6 wing and found the 4 wing on your hint. The 7 and 3 wings proved to be very powerful as well, but not as powerful as your 3467 quad. I'm slowly getting better at finding x-wings and their implications - I'm just a noob, using pairs, triples and quads to find the singles. Hope to climb to the next level (wings, swordfish, empty rectrangles) soon. Any suggestions anyone on how to proceed? Thanks for the lesson Simon! A joy, as always!

[@xThvnd3rstorm]

Absolutely incredible! Figuring out the quadruple seems like a work of art!! After that you could also solve the remaining cells in the affected column/row 5 - afterwards I think it's most elegant to go by strict symmetry! Superb video!

[@stefanholbek2449]

Speechless ... 👍👍👍👍👍

[@blobdffoo819]

Wow i'm very proud having solve this, took me double time as Simon but still very amazing puzzle !

[@Boy314]

truly a unique puzzle. never seen anything like it

[@johnylaw04]

I was stumped and had to watch video up until you showed the xwing with the 7's. Then I was able to solve on my own. Wonderful video, great puzzle.

[@spiveytina]

I don’t know how but I solved this in 23 minutes. I just used pencil marks. I have watched a number of your videos that helped me understand some meanings but I still cannot pick out these x wings or xyz wing things. But wow, you have helped me improve. Thanks!

[@deborahorth5275]

I got it in 10:36, nice puzzle!

[@ChessRabbitt]

Wow! I am doing this puzzle again and I can't get one number.???? 20 mins in so far. Why is that I wonder? Signed confused

[@ssesf]

4 X-wings!!! Looking forward to trying to solve it again in a few weeks.

[@philipcoltharp918]

Indeed, thanks.

[@tinakerr8163]

Instead of pencil marking the x wings on 3467 which is confusing, I found it helpful just to use a colour to mark the different x wings and colour the corresponding digit in the central square, a bit using a legend on a map.

[@sabetwolf]

I spotted the symmetry. I even spotted the x-wings. But the rest of this was so far beyond me I just... wow. Gorgeous.

[@OwlaboveCitylights]

I did in 31:16. Whole things breaks apart if you test the 4s in 3rd row

[@Wecoc1]

Yes! Finally a puzzle about Gurth's Symmetrical Placement! I suggested a Jigsaw some months ago that also had this property (in that case not only givens but regions must also be symmetrical) And once I found a weird Killer Sudoku called Assassin 123 "Roulette" that had this property aswell. Interesting stuff.

[@angelalbericoninojimenez1884]

Increible este Sudoku, que lastima que no este en español, no es igual leer los subtitulos, sin embargo se aprende mucho. Voy a tratar de solucionar este sudoku por mi cuenta a ver que tal me va.

[@Birchbayaromatics]

Loveliest of all puzzles ever...... once I got past the first mind bending logic. I had to leave the puzzle for an hour and come back to it

[@cmonkey63]

I had a dream like this once. One day for dinner we had a lamb roast with way too much garlic, and I spent the night dreaming in feverish logical structures. Unlike my dreams, this puzzle did have an exit. So glad.

[@The_Cali_Dude_88]

A perfect puzzle is correct. ❤