A Sudoku With A Simple But Stunning Trick!

[@bristolrovers27]

You bounced back well after the trampoline emergency... sorry I couldn’t resist

[@hecticdmc]

Yes, he really sprang back into action.

[@anniebean5274]

@@hecticdmc Don't jump to conclusions

[@barbaralevine9048]

How much do we love Simon? His excitement for a puzzle makes me smile every day!

[@kehaarable]

I wish I had something which brought me as much joy as sudoku seemingly gives to Simon!

[@NjniaVanDerWald]

"All i've manage to do so far it's things that are obvious to anybody who gives it a moments thought." Yeah, about that...

[@adblockturnedoff4515]

Yeah. We need to have a serious thought about that.

[@e.m.b.5090]

I can't decide which is my favorite CtC running gag, "There was a emergency" or Simon keeping himself from cussing at the last second and swerving into an extremely British-sounding anger-neologism.

[@mxtchxll]

i wanna hear more about this trampoline emergency

[@evah4431]

Lowkey same It's so cute how you can tell he's got a small child (or several). Trampoline emergency, "I almost made a booboo" in some videos...

[@rourose]

@@evah4431 its super cute when he got to deal with pancake issues

[@evah4431]

@@rourose hahaha, I don't think I saw that one but it sounds adorable

[@Leselampe]

There were also a necklace emergency and a walkie talkie emergency in the last few days😊

[@mrmckenzie0]

Simon has the oddest emergencies.

[@omarelrouby]

I am trying to figure out this new me who literally waits impatiently for sudoku puzzles to be posted at 11:30 PM local time

[@jmbverlag]

Couldn’t you make an update to your sudoku-apps, that it plays your intro-tune everytime you start it? :-) It feels that something is missing, when I start the apps

[@coffeedude]

I think I'd love the apps twice as much if the music played in the main menu

we all like our mozart, i understand

[@stagesol]

I'd rather have Simon saying "Let's get cracking"

[@alantaylor846]

Why not have both? 😸

[@MRafas-ie9zh]

24:10: Missclicks and puts 38 instead of 37 10 seconds later: We trust the pencil marking I almost screamed

[@JuanAlexiis]

I was looking for this comment. Same exact internal scream.

[@petehevans]

I completed it and then went to the end of the video to hear his comments and the 38 pair was the first thing I saw. For a moment I thought I'd gone wrong.

[@oliverolsen1120]

Aad is almost as much on the channel as Mark and Simon

[@spencereades]

The truly unusual day is one in which nothing "Aad" happens.

[@bristolrovers27]

Aad is a great support to this Chanel and his puzzles are quite exceptional

[@evah4431]

Other KZbinrs do ads, CTC does Aads

[@freedortch9278]

@@evah4431 Lol, hey Eva you watch this channel too? Just saw your comment randomly after finding this channel a couple days ago. I recognized your profile pic.

[@evah4431]

@@freedortch9278 FREE? Oh my gods that is amazing, HI!

[@bristolrovers27]

Star of mainstream media now ! Brilliant puzzle, I figured out several ways not to get started and left it to Simon Thanks again to both of you for an excellent Chanel and to these brilliant creators for mind bending puzzles I don’t want to be churlish but could we have the occasional crossword, maybe on a Sunday so we all know what day of the week it is !!!

[@TiaMat99]

Congratulations on the article in The Guardian! That's not just any old town paper... big site! And if any puzzle would have to make the news, it's the Miracle. Lovely to see your channel getting the recognition it deserves! Well done, both of you.

[@covovker]

2:27 Rules 3:11 Lets get cracking

[@Andrew-zi3iw]

you are a hero

[@yahya092]

Congrats on being featured in the guardian guys!! That’s really awesome

[@Derpman_99]

Hey man I just wanted to let you know your videos are really helping me at the moment. I’m going through a really tough break up, and keeping up to date and solving these sudoku’s are really taking my mind off things. Also I can’t sleep at night but when I watch your videos you voice really calms me down and I fall asleep really well, thank you so much for your content 🙏

[@renzojvd]

Same here bro, same here...

[@Derpman_99]

@@renzojvd Just gotta push through my man

[@alkoret]

What's Mark doing on the trampoline?

[@anniebean5274]

making sublime logical leaps

[@davecoleman1265]

Cracking the Cranium, potentially.

[@phs125]

Stop making fun of them, they're our dads!!!

[@markusl.4290]

17:41 Simon: "You can see that 2-4 is not gonna work because of the four here (points at the one above)" Me: But... There's a four literally right next to it

[@12tone]

Great puzzle! Another possible way to get the break-in: You worked out that the outies on the grey rows had to add to 25. Looking at row 3, that means the empty ones have to add to 20, and the only way to do that without a 3 or a 5 is 479. The 7 in box 3 pushes 7 over into r3c2, leaving you with a 49 pair in box 3. That leaves the grey cells as 1268 (plus the 3 that's already there) and since you know that the greys in boxes 2 and 8 must, together, sum to 15, you can eliminate 6 and 8 from there, giving you a 12 pair along with the 68 pair in the upper corners. Then r3c3 can't be 6 because that would make the greys in box 4 add to 10, which means the greys in box 6 would be 5. With an 8, the remaining greys in column 3 must be 125, so the box-6 greys must add to 7, making them 124 and giving you a 7 in the bottom corner. Writing it out like that looks a bit awkward, but and I'm not saying it's a _better_ technique than yours, I just liked the way it flowed when I found it so I thought I'd share! EDIT: Oh, also, another way to place the central 9: Once you have all that, you've established that columns 3 and 7 and rows 3 and 7 all have 9s in their outies, so from the 49 pair you got in box 3 you can sort of windmill your Snyder notation 9s around the grid, restricting them to two spots in each of the corner boxes. Importantly, all those spots are off the diagonal, which means both the diagonals need their 9 to be in the center box, so it has to be in r5c5.

[@t71024]

Yet another break-in strategy: Along the mandatory 12386 and 12359 combos, it would be very difficult to put two 9's in the grey area (I think I tried all possibilities, nothing worked). Therefore, the 9 in the center box must be in the center cell and cover both diagonals. Otherwise at least one other 9 would be needed on the diagonals near the corners of the grid, and because of the Phistomefel constraint, each 9 in the corners would have a doppelganger in the perimeter of the grey area.

[@nijram15]

I was telling my friends about CTC (and how wholesome it is) and it turns out one of my friends is actually teammates with the daughter of Aad! What a small world :)

[@nigeljuggler]

CTC - Oh I guess you mean Cruising the Cut, a wonderful KZbin Channel if you like canal boats.

[@aadvandewetering6486]

Ah, nice, I have more than one ...

[@markusl.4290]

48:46 solved Incredibly hard to start but after juggling with the logic you can see that there is a particular soultion. Wonderful

[@emmacrisp5926]

I solved it before watching the video, without having to bifurcate!!! i'm so proud of myself!!!!

[@lmelior]

"A bit slow to get the corner trick" If that was slow, I was moving glacially.

[@GodShiru]

I like doing the puzzles first, so I can feel smart when Simon or Mark are stumped while I managed to find the solution. Then I look at their time and mine and feel dumb again... 58:05

[@fvni]

You are the best in speaking out the logic for the audience on every puzzle - all levels of solvers can understand what the thought process is without getting lost - it is not an easy feat.

[@sysy1481]

Randomly came across your channel and now im totally hooked!!! Amazing content!!

[@poetsinlove]

Hi Simon, Mark, & all the wonderful testers - This channel has been incredible since I found you around a week ago. I’ve been having trouble sleeping lately, and this channel is so soothing - it’s been helping me wind down for bed each night. I never thought sudoku would be the content I’m looking for on KZbin, but you obviously have proved me wrong. I appreciate Simon’s amazing explanations of his solutions and logic. Keep on cracking!

[@amandaking9527]

I literally didn't know the rules of sudoku until I started watching your channel yesterday. Now I'm addicted to these because I randomly got recommended a video and thought I'd finally try to learn. It's so satisfying to watch and your voice and the sound of the keyboard is so relaxing!

[@nadavbenjamin9029]

I majored music in high school, and we had a tradition where every year the music seniors would put on a play at the end of the year. Obviously we were the actors, but we also chose the soundtrack and play it live during the show (we even composed some original pieces for it). My point is, my class decided to do Cyrano de Bergerac, so hearing Simon say that at 16:44 made me very nostalgic and happy. I played the role of Christian de Neuvillette, and pretty well if I do say so myself :)

[@arthurvanobost7381]

The 7 you put at 15:22 was the first digit I managed to enter. Because the 3 blank cells have to sum to 20. (45-20-5). The only way to make 20 in this row is 4-7-9.

[@keskinyavuz]

same for me

[@xarmanhskafragos2516]

Sometimes i think how beautiful those puzzles are. They dont require any background. You can literally go to ancient Greece and enchant every philosopher there with them. Truly magnificent and i wish every human in the last 3 thousands years had a chance to solve them.

[@shifu591]

You just give off good vibes thanks for making my day:D

[@Hectorlph]

Despite not being able to figure out 95% of the logic in these puzzles you show, they are always a delight to watch regardless.

[@michael___684]

your idea about 55-45 helped me break open the puzzle. no idea, how long i would have been sat there otherwise. Great work!

[@jonchambers131]

38:00, really pleased about that, I actually found completing the grey box quite easy then got bogged down with the remaining sudoku. You pretty much need to step back and do the 20+20+20+20+45-100 trick to get the corners; can't imagine how you could progress otherwise. Fortunately I remembered a recent(?) puzzle which needed a similar technique so I was primed to check that. I actually got the top grey line before getting the corners; any grey line has to have 2 or 4 odd numbers for parity. Couldn't be 4 as 1+3+7+9 would add to 20 before you added in the lone even, and it was pretty easy to dismiss pairing the 3 with a 7 or 9 because you'd then need to get either 8 or 10 using just evens; no way. Once you know it's 1 and 3 and three evens it's easy to figure out you have to drop the 4.

[@zekicansamli5614]

I found the 7 next to the 5 in C1R3. Then, I stuck. I thought it has to do something with the sum of the squares, but could not figure out the corners.. Amazing.

[@jamestaylor961]

Love the trampoline emergency interruption and the Cyrano de Bergerac comment! These videos make my days.

[@HULKEN1UP]

"some times my life gets in the way!...you Sir are just one classy act!

[@rach6088]

need more info on the trampoline emergency

[@izansmallcat631]

You should change this channel name to Cracking de Wetering at this point lol

[@TiaMat99]

LOL! Alternatively named: "What has that crazy Dutch guy made for us now?"

[@glum_hippo]

I would be here for that!

[@lgrillo]

I love watching these and observing how his brain works, the strategies he employs and how he methodically susses out the answers. And then I got try one on my own and depression sinks in, LOL!

[@robb1267]

In addition to my thorough enjoyment of the sudoku, I'm also enjoying the various emergencies. In recent memory, I count a necklace emergency and now a trampoline emergency. :)

[@schetefan24]

There's also been a Walki-Talkie emergency ;)

[@ukdavepianoman]

What a puzzle. The 3 grey corners have to add to 21, look. Once I'd disambiguated these, I was cooking with gas. I got the 9 in the centre but took an age to remember the remaining up and down grey cells must total 11 and so were 1-2-3-5. A lot of fun solving this.

[@stevel875]

I focused on different areas to Simon for most of my solve... got the 15s as 3x20-45, did edges of grey box to imply the corners, and after placing 8s in grey box, spent a lot of time working through possible combinations adding to 25 on the outsides only deducing the position of the 9 in the central box from where the 9s went on the outside. When the correct path finally emerged I had a feeling of having beaten the puzzle into submission rather than finding the solution. Made a stupid mistake that broke the puzzle for me (entered 58 wrong way round, but didn't spot that, only the later contradiction when I finally entered the 4 into the right place in column 8). I then watched Simon, and marvelled at the sheer elegance of the "correct" solving path.

[@kieronrushton527]

I love watching your videos when I'm bored and finishing my uni work at 4am

[@malutj]

I'm proud to say I spotted the trick with the four corners summing to 25 very quickly! I'd watched Simon use that strategy on past puzzles and it just jumped out at me.

[@04LightningFan]

That was so good! It took me a while, but I'm satisfied that I was on the correct solution path and finished the puzzle. When I realized I could figure out the corners of the gray box, I was very happy with myself.

[@weedhopperpress4755]

I made some headway on my own, but completely missed the first thing Simon noticed (the central quadruplet). That cracked it wide open for me. I love when that happens: I get to feel smart for finding something before Mark or Simon, and also get to appreciate their brilliance in heading right toward the puzzle's weaknesses.

[@francescopetracca374]

This was a masterpiece one year ago and it is still a masterpiece today with all the new techniques discovered. Hats off to Aad. (and finally I solved it too 😁)

[@Tyiriel]

>IT'S JUST.. Say it... >BEAUTIFUL, MIND BOGGLING, STUNNING

[@piarittersporn]

Thanks for the start-up help. It took me a while to understand how the corners of the gray square were calculated.

[@lakarto19]

Brilliant, elegant masterpiece from one of my favorite setters. Spotted the corner cell trick relatively quickly, and managed to solve in 18:29.

[@Keyboardje]

Wow! Well done :)

[@slinox5069]

I love watching you. You always have so much fun solving these puzzles :D

[@Stuartdouglas19]

there is NO WAY I would have solved this at the start of lockdown. still took me a while to spot all the doubles and triples and their knock on effectd, but still. great channel, and the methods taught here really do help with the logic of lots of puzzles

[@evah4431]

Just solved it in 1h20m. I'm very happy that I managed to figure out the trick on my own without of having to check the video! The recent coloured "equal sum" sudoku really burned me by having me spend half a day just to get it wrong in the end, now I'll always think about what the sums of everything have to be...

[@jeroennouwens9972]

I want to talk about part of the solve I did that was just beautiful, but it turned out to be unnecessary. So... We start with the 2 7s placed, the ones in boxes 1 and 9, and the 68 pair figured out in row 3. Now we note that the 9 could never be a part of the edge of the gray box, since the numbers get too high in the 20 sum. This means that in row 3 and 7 and columns 3 and 7, the 9s are outside the boxes. But in box 1, the 9 is now forced into column 3. Therefore the 9 is forced into row 7 in box 7, and in column 7 in box 9 and finally in row 3 in box 3. Finally, we note that the 7 is never part of the diagonal in either of those boxes, so in the centre box, the 9 has to be part of both the diagonals, forcing it in the centre. I just loved that idea so much, with all the symmetry going on, I had to comment on it.

[@belmusege]

I did that too, the 9 was litteraly the first digit I put in the central box. So when I saw Simon's solution I was just "well okay... That's quicker ^^." But I like this way too.

[@PH34RB]

The 25 trick also applies to the 4 corners of box 5, forcing 8 and 7 to another 2 offset corners, and thus 9 to the center. It's redundant by the time you get there, but by the same token it's really neat.

[@leporid257]

i had a different path because i *pencilmarked* (gasp) a bunch of sums. but i think the diagonals also force the 4 corner digits to rotate.

[@pandacademy9398]

This one smacked me. Took me over an hour. Dang. I did get to use that unique logic about the 4 2x2 boxes in the corners being the same numbers as the ring around the center though! The intended solve was brilliant though! I didn't see that at all!

[@sudokanard]

I did it in 38 minutes. It took sometimes to spot this variation on a trick sometimes seen on Killer Sudoku puzzles. Impressive puzzle as usual by this Grandmaster.

[@leyubar1]

When he says there is a trampoline emergency, do you imagine he has kids, or do you imagine there are bad guys bouncing through the streets and the mayor of Gotham city is shining a light with a massive sudoku into the sky to summon him?

[@evah4431]

I really Aad-ore this guy's puzzles. (Da-dum tss!)

[@florianbabel5558]

I had to think about Phistomefels logic from a few weeks ago when he talked about the 55 in the ring, because I discovered that the 2x2 corners all sum to 55

[@robertr7923]

and you could use the fact that there were no 9's in the outer ring, so the 2x2x corners couldnt either.

[@williamperezhernandez7331]

Which places the 9 in central cell, it must be on both diagonals and in the grey cells.

[@richardglover314]

Yes I remembered that and thought that was the trick we were meant to see. Anyway I gave in and just watched the the Simon Solve.

[@KalOrtPor]

I think either way works to the same end, I saw the central box being 45 meaning the perimeter would be 55, and that adding the 4 outside rows together makes 80 and would leave 25 in the corners from being double-counted, a trick we saw using the whole grid in past puzzles. From there, with the given 4 it's not hard to find the 3 corners totaling 21. Knowing which unique combinations make certain sums of cells was absolutely essential to solving, an expert like Simon knows them by heart like the 1-2-3-5 for 11 combination, one that's also stuck with me from before, but a lot of others I found myself consulting charts to speed things up instead of mentally going through all the possibilities which is tough to keep track of. I did some cleanup on the cells outside the gray columns and rows this way.

[@minimonkey252]

an hour and 36 minutes on this, I'm exhausted. I felt desperate so many times. Real clever puzzle.

[@Painkiller1430]

At the beggining you can find the numbers outside the gray area in row 3. Their sum is 45-20=25. We already have a 5. So 20 without using 3 and 5 can only be 4_7_9. 7 goes next to the 5 and 4&9 make a pair in the 3rd box at the end of the row :)

[@rodrigopenaranda8553]

Plsss , you and Mark neeed to do a Q&A

[@JuanMataCFC]

i believe they did one quite recently. early 2020 if i'm not mistaken.

[@inwalters]

maybe when they reach 200k subscribers

[@DawnDavidson]

This is one of those times when my gut said “the 9 has to go in the center” but I couldn’t figure out WHY. It was great to have my hunch confirmed though. Otherwise, no way I would have figured out all the other logic. Very fun to watch Simon do it though!

[@TheNewAccount2008]

Great puzzle, wouldn't ever have been able to solve that.

[@joshuajones2066]

Your so passionate and have so much fun with these, it’s neat watching you guys.

[@joelbaker210]

Solver: "This is really hard. You might have to bifurcate." Simon: "Hold my beer."

[@etherealicer]

The solver should go and watch cracking the cryptic... all is there (the trick with the outer grey ring is very much the same to a recent killer sudoku).

[@jazoumiddel]

I don't know why, but I really like to watch these video's of you solving all sorts of Sudoku's! It's kind of meditating to watch :P

[@JoeObie]

I wish I got as excited for anything as Simon does for puzzle elegance.

[@zalibecquerel3463]

I did very well on this, using the technique that "the digits making up the outer grey ring, must appear in the four 2x2 areas in the corners of the grid". You'll end up with 4x1s, 3x2s, 2x3s, 2x4s, 2x5s, and one each of 6, 7 and 8 (or therabouts). This rule was explained a few weeks ago in a video.

[@MrXami08]

I did the same but just with lack of 9s! After seeing 9 couldn't go in the outer ring and have enough 1235s for the middle box then it meant no 2x2 corners which meant it had to be in the dead center to get both diagonals valid

[@vderiem]

Nice one! I took a different path after 12:50, noting that the 9s can't lie in the outer grey ring in boxes 2,4,6 and 8 either because this would put too many 1,2,3 and 5s in the center box. Looking at rows 3,4,5,6 and 7, there is a jelly fish of 9s outside the grey region (one of the five rows has the 9 in the center box, but it doesn't matter which one) that rules out 9s from the main diagonals in boxes 1,3,7 and 9. By diagonal constraint, the 9 in the center box must lie in the center. Hence his neighbours are a 1,2,3,5 quadruple and the corners a 4,6,7,8 quadruple that gave me a good restriction on the main diagonals from which the rest of the resolution based itself on.

[@adamheywood113]

Tried working out the possibles for the left and bottom grey columns, they both contain a 4 and so you need to make four digits add up to 16. 1, 3, 5, 7 will do it, so will 2, 3, 5, 6. Couldn't see any way to narrow anything down further than that, I don't think I'll bother. Really like your channel btw, such a robustly simple system. Thank you for making such great content.

[@yomommasofine]

Watching you solve puzzles makes me feel smart. We did it!

[@Draedaja]

Wow, that got surprisingly exciting near the end there, with the "3 7 pair" that somehow changed into a 3 8 pair as it was typed in ;)

[@jaeusa160]

I really don't have the time to do these myself but I do wonder how useful it might've been with some of the early available digits to focus on the 4-tile sections outside the grey square and the fact that they all need to be 4-digit combinations which sum to 25, particularly with the three given 8s in boxes 2 5 and 8, and boxes 2 and 8 seeing each other.

[@bob53135]

Row 3 coud have been restrained from the start, as its 3 white cells sums to 45-5-20=20, and 20 without 3 and 5 must be 9+7+4. The grey cells now are 12368, which put 8 in on of the corners. Later, when we now the 4 corners add to 25, it can only be a 6 in one of the top grey corners, and then a 7 bottom right.

[@someguy-k2h]

The key piece, was corners and subtractions. That broke the whole thing open. Until I saw that, I was going to start bifurcating on 8's and 9's. Really a great challenge. Thanks so much.

[@Sirakle]

Another fascinating puzzle! I discovered another solution partly by mistake, so I don’t know if this counts. What cracked the puzzle for me was discovering that the nines cannot go in the outer rows and columns of the grey box. A row or a column with a four cannot contain a nine, because you cannot make the remaining seven with three numbers without using a four. That excludes the bottom row and the left column. The top row must contain he digits 12368, because of the five to the left. That puts the seven next to the five, and a four-nine pair in the third box. The right column could contain a nine, but then you cannot place a seven anywhere in the central box. Why? Because wherever you put the seven in the central box (it has to go in the centre in this case, but I won’t get into that) you have to have one row and one column add up to 20 with a seven in it, and you cannot do that without using a four in both cases. But you cannot put another four anywhere in the outer rows or columns of the grey box (you cannot have a four with a nine in the right column, the four in the corner excludes the left column and bottom row, and the top row does not contain a four.) Which means you would have to put both fours in the central box, which of course breaks the puzzle. The nines in row three and seven and column three and seven now has to be outside the grey box. The four-nine pair resolves that in such a way that the nines now cannot go in the diagonal in box one, three, seven or nine. Which means that the nine of both diagonals have to go in the central box, where they intersect. That cracked the puzzle for me.

[@didierribeiro7832]

Hi. Will you solve the second miracle sudoku from yesterday ?(the one with thermo sudoku) it making me crazy.

[@null6955]

yes seconded!

[@nadeemhajiiqbal9214]

I tried it. The only progress I made was that both bulbs can't be the same number. Coz whatever that number is, placing it in both bulbs would rule out all the cells in Box 5. Good luck though.

[@KalOrtPor]

The ringfence around a digit thought process from the first miracle puzzle comes in handy. Also, because the 3-therm can't have consecutive digits, it limits the base to 12345, the middle to 34567, and the end to 56789. Then you start noticing things like 1-2 can only be in the base and 8-9 only in the end. This is definitely the toughest part, just getting started. One thing to try is starting with 5 as the base since it hardfixes the therm digits and then seeing where that takes you, as testing placements of digits will no doubt be needed to rule possibilities out.

[@yichen6313]

Beautiful puzzle and a nice solve! I notice the ring and so I used the Phistomefel's trick to get the 55. But it's just the difference between grey and box 5 as Simon pointed out :D Feeling dumb now...

[@deleetiusproductions3497]

“Everything should be made as simple as possible, but not simpler.” -Albert Einstein

[@londov1]

I don't understand the deduction at 20:46. Why does not having a 3 in c8r8 mean there's no 3 in c9r1? How would it break if the 3 was in c8r4 and in c9r1?

[@lauraschmidt5516]

quarantine became that much more bearable because of this man

[@AnRuixuan]

Felt proud that I spotted the corner trick right away!

[@stevesebzda570]

Triples were used nicely in this one (and I noticed things that could be used against them I'm noticing). Always wondered more about those triples. An absolutely cool one you're right lol

[@NuttyFalcon]

I love your solutions. Could you please further explain the 9 placed at 25:09? I see this type of set-up in a lot of my puzzles and want to understand the short cut.

[@RichSmith77]

Do you mean the 9 on the bottom row? (Described from 24:50 and placed at 25:01). 3, 7 and 9 are the last remaining digits required to complete row 9, but the empty cell at the bottom of column 4 already sees a 3 and a 7 in the column, so it can be neither of those. Therefore it has to be 9. It's what is often called a 'naked single'. 9 is the only digit from 1-9 not already seen by the cell in the row, column or box. This type of naked single is usually fairly easy to spot because most of the other candidates are already in the same row. Any row, column or box that already has 5 or more digits already entered (the more the better) it's usually worth mentally working out what the short list of digits is that are required to complete the row, column or box; and then see if any of the empty cells see all but one of those digits somewhere else. In this case, row 9 already has 6 digits filled. It can quickly be determined that it's missing 3, 7 and 9. So you then scan each of the columns 3, 4 and 7 to see if any of them contain the missing digits 3, 7 or 9. Row 4 is seen to contain two of them: 3 and 7. So only 9 can go in row 9, column 4.

[@agilby1512]

The surrounding box must equal 55 is what made everything click for me! So obvious in retrospect.

[@thomasgrubb5400]

Here's a start to a different solution path. You can fairly easily rule out 9's from the border of the 5x5 grey cells. This comes from the fact that the only way to get to 20 with 5 distinct numbers, including a 9, is 1+2+3+5+9 = 20. This rules out the border strips with a 4, the top border strip is ruled out by the 5 in the row, and the rightmost border strip is ruled out by examining the interplay between a supposed 9 in this strip and the 9 that must occur in the center 3x3 box. Because of this, there are no 9's in this border strip, and hence no 9's in any of the 2x2 corner boxes (using the equivalence between these 16 boxes with the 16 boxes surrounding the center 3x3 discussed in a previous video). Hence the center box must be 9 to satisfy both diagonal constraints. This gives a 1235 quadruple in the "t-shape" surrounding the 9, which allows a fairly straightforward solve afterwards.

[@MubarkAlKhatlan]

1:40:00 I'm proud of myself.

[@antonioliles5027]

Hell yeah man! That is about how long it took me as well and with puzzles like this, I am amazed that I can even do them at all!

[@everythingcoffee8901]

I quit after an hour. I applaud you. *clapclap*

[@mbakenemdusink9757]

It took me 1:25 to find out that I totally screwed up the whole thing right at the beginning :-)

[@moonglum101]

I think it took me forty minutes or more to realise the trick with corners of the grey box. Even after that I still took a total of an hour and thirty-three minutes. So, pretty similar time.

[@TimCamilleri]

I didn't watch this one when it was released. Lovely to see a puzzle from the days before we knew about the Phistomefel Ring :-)

[@izmayaya7693]

I randomly found this channel on my frontpage and I love watching your videos :D

[@omo-wd2zq]

I used the nice trick you mentioned in your video "Brand new sudoku trick you wont believe" from april 21st to place the 9 in the center square as the first digit. After figuring out that the grey corner pieces are 678 its clear that all other grey edge pieces couldn't contain a 9 either(it would easily break the 20 sum). So the whole grey edge does not contain a 9 and therefore all 4 little 2x2 squares in block 1, 3, 7 and 9(see mentioned video) do not contain a 9. So where does the 9 go on both diagionals? Both of them have to have their 9s in block 5, so the 9 is in the center square. This trick also helped later on placing the 8 and some 1s.

[@poohssmartbrother1146]

2 hours. granted I stopped for restroom break. I actually opened Notepad and figured out all the possible 5 digit combinations that make 20. That helped loads. The twisted 8 xwing helped too

[@johnblazer7661]

I tried it and caught myself thinking in an English accent.

[@220bea]

Hahahaha. Me literally every time 🤣

[@jaymant2658]

What technique was applied at 20:40 to remove 3 from the central square? I've watched it several times over and can't figure out the logic.

[@jaymant2658]

Figured it out. For anyone who made the same mistake as me, the 7th column needed only the digits 3 and 9. Because of this, 3 could not be anywhere else in the box, including the central square.

[@nickwoollon9855]

Wow good timing to finish yesterdays puzzle, 3 minutes after this one was uploaded!

[@lawskuboi]

I actually screamed when you pencilled in the incorrect numbers

[@cyrus5237]

My first sudoku video. Nice work!

[@ArunIyerS]

If we look at the final solve, the four digits in the four corners of the sudoku sum to 55 (exactly the amount in the boundary of the grey square) which reminded me the result that phistomefel (I think) had proposed several videos back. I was wondering whether one could have used that result here to solve it in a different way.

[@covovker]

My first digit was in row 3. Its sum of 20 for the rest 3 digits is restricted to only 974 (965 can't be because of 5, 938 because of 3, 875 because of 5). Which put a 7 into (2;3) right away because of the 7 in the right most square. And it does not seem to be a coincidence that it has exactly those combinations excluded by other digits of the grid.

[@thomads3890]

ah, me too! :-D i posted a couple of comments about that