A Brilliant (And Beautiful) Killer Sudoku

You can try this incredible puzzle here:
app.crackingth...
Simon attempts to solve this beautiful killer Sudoku created by Gaurav K. Jain for the Indian edition of the World Sudoku Grand Prix 2019.
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▶SOFTWARE◀
We mainly use Duncan's Sudoku Solver, which is available at www.littlegogs....
▶ABOUT US◀
Hi! We're Simon Anthony and Mark Goodliffe, two of the UK's most enthusiastic puzzle solvers. We have both represented the UK at the World Sudoku Championships and the World Puzzle Championships. We're also "cryptic crossword" aficionados. Mark is the eleven-time winner of The Times championship and Simon is the former record holder for most consecutive correct solutions to The Listener crossword. We hope we can help your puzzle solving while also introducing you to some of the world's best puzzles.
Thank you for watching!
Simon and Mark

[@jacobknight5497]

Managed to finish in 59:24 with no hints. extremely proud of myself!!

[@pedroslots184]

Seeing the joy you get from a great puzzle is almost as good to watch as the solve itself.

[@sabriath]

I was staring at the 1 in the top right box for the longest time like "is he going to notice it?" Nope, you didn't.

[@nicokuhne3255]

Robert Caldwell i normally don’t care if he doesn’t see a number, since it’s impossible to see everything, but that god forsaken 2 was resolvable by like 12 ways. Then he says „oh and finally that 1 resolves this, NOOO not finally, every number resolves it, literally every other number resolved that square

[@diddyman1958]

me too :)

[@itsmeagain1745]

Sitting here shouting '1' at the screen - lock-down fever me thinks... (April 2020)

[@astralm8072]

Also "I don't like the way that 9 is sitting there in the corner there, let me get rid of that" killed me near the end

[@samurai3502]

You could add every number in the grid to figure out the center 1, though it wasn't helpful.

[@perry4754]

You can also do the sum modulo 10 to make the math a little easier.

[@toddbiesel4288]

Matthew Schulz That would be the rarely-used Rule of 405.

[@bluefloyd1]

It wasn't a waste of time for me, that's how I got in

[@mhelvens]

At some point, I felt like I could deduce some pairs based on how symmetric the Sudoku had been up to that point. Like: "If there isn't a 12 in this cell, the puzzle is not as beautiful as it could be. Ergo, there is a 12 here." 😆

[@Austin101123]

13:20 you can figure that the center square is a one from the very beginning. The sum of the whole board must be 405, and we have 404 accounted in all but the center square.

[@uhmarcel7417]

I saw that logic at the beginning too, but I thought "no way im adding all this stuff, lets hope it appears along the way" xD

[@shane8037]

lol no way I can do a killer without the benefit of the tools on DKS website... I'd take ten minutes calculating how many ways you could make 14 with three numbers then still mess it up

[@sdrawkcab190]

Yeah same here.

[@RandomBurfness]

Then you're approaching killer sudoku puzzles in the wrong way. Focus on the cages with just two cells in them. When you can restrict bigger cages such that you know there must be one digit, then you can just take that number away and you're faced with a much easier problem. No killer sudoku demands you to know each of the ways you can make 14 in three cells, but say you know there must be an 8 in a 14 cage with three cells, then you are left with the much easier problem of figuring out how you can make 14 - 8 = 6 in two cells, and you can only do that with 1 + 5 or 2 + 4. Similarly, if you have a very large cage that you can subdivide into smaller cages, then you've again limited the analysis you have to do. Some value/cell combinations are worth knowing though, such as knowing that 8 in three cells can only be done with 1 + 2 + 5 or 1 + 3 + 4, or knowing that 10 in four cells can only be done using 1 + 2 + 3 + 4, or 21 in six cells has to be 1 + 2 + 3 + 4 + 5 + 6, and so on. But you'll find plenty of killer sudokus that'll teach you this fundamental knowledge, so you should be good to go.

[@danpowell806]

@@RandomBurfness I don't think that telling people they're doing things wrong is effective. And also, many people have trouble knowing things like "X in Y cells including/excluding can be..." while also holding the relevant logic in their head.

[@supermills03]

I had to pull up the site to use the calculator

[@BVIGrockle]

This is one of the many reasons I love this channel. Occasionally checking puzzles from the back catalogue you've not solved and finding gems!

[@Pyromonkey83]

Wow... Well over an hour for me before I figured this out. Brilliant puzzle, awesome solve. Well done!

[@Matilda_the_Hun]

I watch all your videos but I love your killer sudoku solves the most!

[@matts3178]

15 minutes for the world's best solvers... I did it in a solid 160.

[@sircheesethethird6179]

the more, the merrier.

[@Jamm3z133]

That 2 in the 8 cage in the mid lower left was so pivotal, I struggled for about 2 hours with this puzzle because I knew that once I cracked the double X wing of 1s and 2s it would be more straight forward, quite tricky all in all! You make it look easy as always

[@tiemen596]

I finished it in about 35 minutes. Proud of it :P. It is funny to see how much more efficient you are. I managed to find all the corner squares and the central square before anything else, going through some logic that was much more convoluted than necessary. On the central one I found it as follows (4:20 marking as starting point): - Looking at columns 1 through 4 and the boxes they contain, 6 cells stick out: r2c5, r2c6, r2c7, r8c5, r8c6, r8c7. Arithmetic shows that they must add up to 25. - Looking at columns 6 through 9 and the boxes they contain, 6 cells stick out: r2c5, r2c4, r2c3, r8c5, r8c4, r8c3. Arithmetic shows that they must add up to 24. Since all above cells are contained in the 21 box in row 2, plus the 23 box in row in row 8, we can deduce that the sum of r2c5 and r2c8 = (25+24)-(21+23) = 5. So they must be 2 and 3 and the central square is a 1.

[@joelbaker210]

It took me 35:58. One thing that was fairly obvious that Simon didn't notice (yay me!) was the given 9 in r1c1 was in a 20 cage meaning the other 4 digits in that cage added to 11 which is an automatic 1-2-3-5 (in some order). This was particularly useful given that r1c2 was already restricted to 12 so the 3 and 5 were contained in c1 and helped to disambiguate along that column, etc.

[@joelbaker210]

Edit: the 9 in r1c1 wasn't a given but I had entered it early on.

[@SvviftDeath]

21:15 , You forgot you set the 9 there in the corner to notate it was the only two places a 9 could go. You could've used that logic to immediately place the 9 in the square instead of getting rid of it.

[@danpowell806]

Worth note: All of the cages and the four givens add to 404- you can deduce the central 1 immediately.

[@hhaavvvvii]

Adding all of that up is way too slow though.

[@Jonnysh]

I've started doing killer sodokus on dailykillersudoku and i thought that would prepare me for this puzzle. instead, i found out that I'm using the combo generators as a crutch.

[@vidaroni]

Oof, same here. Working without it was painful. So I opened the site in a second window and used their combo calculator. 😳

[@Jonnysh]

@@vidaroni that's exactly the kind of problem solving I expect to find on this channel, props!

[@zacharyfitts9232]

60 minutes in and i had 2 numbers in the grid. happy to see they were right but there were so many simple things you did that i just completely missed. what a beautiful puzzle

[@InfernalMachinePict]

Is the "Check" button not fully working yet? I have the same answer as Simon, and at first it kept telling me it wasn't quite right. But if I kept clicking the button, it then told me it looked good. Now it's back to telling me it's wrong. Other than that, the new improved web app is much easier to use, and really adds value to the channel. Well done!

[@tallrapp]

Agree. The check button said my solution was wrong, so I watched the video and saw the same answer in the end. Clearly something wrong with the check button.

[@Czeckie]

even though im generally bad at killer sudoku, im doubly as bad with this, since I overly rely on the functionality provided by daily killer sudoku web app

[@HairySand]

It took me about 1 and a half hours to complete it. I had never heard of this type of Sudoku before watching your channel and this is the first one I have ever tried. I really enjoyed solving it. (Now I need to give cryptic crosswords a chance, I had never heard of those either!)

[@slythawyrda]

I think I used about 2 to 2.5 hrs on it, but I did make a mistake that cost a bunch of time before I noticed it, I had somehow swapped the 3 and 7 in row 9.

[@rebellucyanne]

these things take me hours, but im always happy to have gone through 2 plus hours all the way to the end with no mistake

[@Gille28]

I really liked this killer sudoku. Took me 55 minutes to solve. I also like the changes to the website. This way it's easier to solve on a tablet, since I can change more quickly to the number input I want!

[@killroy42]

When you put "46" in that cage, I thought I was wrong and rewound and re-watched... thankfully you saw it and I'm not going crazy just yet :D

[@wowwee8562]

That was incredibly satisfying

[@lottebronable]

Hey, I tried solving the puzzle using the link and used the "check" option to check if I was on the right path. At one point I was stuck and saw that I had made a lot of mistakes when comparing it to the video. Even though the "check" option didn't show that the number I had put in were false. It only colored the boxes red that didn't contain a "normal" number. Hope you can solves this, because the check option helps me understand and learn these kind of puzzles by spotting the mistakes early on 🙂. Thank you for creating the program en uploading all these different types of puzzles!

[@danpowell806]

The 'check' button on the app only looks for duplicates in a row, column, or 3x3 box, it doesn't check cage totals, cage uniqueness, or correctness to the solution.

[@cliffthecrafter]

When I solved the puzzle, the first number I placed was the 1 in the center. I used the 45 rule to find the first x-wing, which eliminated 1 from two positions in the middle row, and since a 1 in the 9 cage would mean a repeated 8 and a 1 in the 10 cage would mean a repeated 9, the 1 in the middle row had to be in the center.

[@callumvlex7059]

The first thing I filled in was the 1 in the middle: All the squares in a sudoku add up to 405, so you can count them up (caring only about the units not the 10s or 100s) and when you get 4, you know you're left with a 1 in the middle.

[@lynnrinzz]

Not sure what the Check in your site is supposed to do but if its to check for incorrect numbers like in the daily killer sudoku site, it's not working right! But if its just to check if the puzzle is completed then I think it's doing its job fine :) Also really liking the new layout, much easier to toggle between notations! always enjoying your videos!!

[@Magicsquarepuzzles]

Killer Sudoku is a really great puzzle. Sudoku is addictive. The Killer Sudoku is devastatingly addictive. Solving these puzzles is like doing meditation. I wonder why this killer sudoku is not popular like Sudoku.

[@goldenera7090]

beautiful puzzle , brilliant solve Simon, why don't you participate in these Championships?

[@paulknox999]

I am 3 hours and still counting :) my first ever killer

[@yatagarasu1495]

yes, i love watching u solving killer sudokus. i cant do them for shit cause i am dumb AF but always fun to see them

[@shane8037]

I feel your pain. Do the easy ones on daily killer sudoku, though, they are possible even for monkeys like us with their little calculators on the side.

[@yatagarasu1495]

@@shane8037gonna blast my head off on them tomorrow

[@shane8037]

@@yatagarasu1495 stay safe bro

[@yatagarasu1495]

@@shane8037 i did it today, its the level 2 one i needed 48 minutes lmao

[@shane8037]

@@yatagarasu1495 but you did it and that's what counts!

[@neomorphicduck]

I'm wondering about your notation. You sometimes pencil numbers directly into the center, and other times you pencil numbers into a grid arrangement. What's your reason for penciling using each of these methods?

[@jkid1134]

Duck Osborne when he pencils into the middle, he’s intending to note that a cell has been limited to exactly those values. When he notates in the corners, he’s keeping track of the only (typically two) locations inside a 3x3 where a particular value can go (referred to here as Snyder notation)

[@danpowell806]

Center notation is "These are the only numbers that can be in this cell", corner notation is "these are the only cells in this region that these numbers can be in".

[@igoretski]

I needed 58 minutes 4 seconds, but must admit, I was playing a lot of killer sudoku lately. I had many unresolved pairs or two possible options for a long time.

[@ericpraline1302]

Great puzzle, very much enjoyed that. The 21 and 23 clues seemed redundant.

[@toddbiesel4288]

You don't see these kind of puzzles every day with some givens in the grid.

[@Jouzou87]

Had to restart this maybe like 5 times because I always got it wrong. Finally solved it!

[@robdylan4]

I needed 3-4 tipps on how to think about these killer sudokus to get through this one. Very nice puzzle though

[@jozin457]

Haven't done even a regular sudoku in years...53 and a half minutes is not a bad results for me for this one

[@jgard1990]

Took me one second under two hours, slow, but it was a fun, and my first ever cage sudoku.

[@freddiehand6551]

11:39 you could have worked out R9C7 couldn’t be a 4 or a 9 ages ago from the 49 pair in the cell!

[@RandomBurfness]

I did this in 25 minutes! Lovely puzzle.

[@RandomBurfness]

I saw something else about the puzzle. The first digits I managed to place were in the positions r1c1, r1c9, r9c1, r9c9, and r5c5. In other words, in the 3x3 block at coordinates (x, y), you could solve the cell that was in position (x, y) of the very same 3x3 block as your first moves in the puzzle. Good stuff!

[@honigschlecker1]

31 min. for me - not too bad. 😊

[@julianogodoy964]

Cages are ridiculously symmetric in this Killer huh.

[@AdelElAtawy]

I really can't see how this puzzle is considered hard... It was a pretty straight forward one.. medium may be. Without trying to go super fast and was still 14:xx puzzle !! (But to be fair, I am faster with killer Sudoku than regular)

[@kevgermany]

Col 9. As soon as you got the 13 in top right box, bottom right had to have remaining set of numbers to come to 13, which then needed the 7, giving yo the missing numbers in col 7 of that box. Impressed by your speed, but a little more thoroughness would improve times. Ended up with new version of your software. Once I put a normal number in a cell, wasn't able to clear it, could only replace. Seems to me that corner, centre, colours are too many ways of doing the same thing. And confusing. E.g. top right box col 7, you mixed centre and corner numbers. This meant the 9 in the corners got missed, then duplicated. Better to centre the numbers and colour if needed. But there's the danger of over complex pencil marks if abused.

[@kgy121]

On the app, it claims the nine box in the middle is full of 1 and 7. That doesn't seem quite right.

[@RoderickEtheria]

Wasn't too difficult. One of the major things to realize about this puzzle is something you learn based on Jigsaw Sudokus, where you realize the numbers in the centers of the first and ninth columns have to be the same as the numbers in at the top and bottom of the second and eight columns. Don't know why it defeated him, unless he gave himself a time limit before giving up. I didn't have to use any fancy techniques really, not like swordfishes or anything.

[@keeegz95]

given he did it at the grand prix i would say he did give himself a time limit, also being under pressure probably slightly harder to think

[@slythawyrda]

Did you mean the edge numbers in the 4th and 6th row have to be the same as top and bottom of 2nd and 8th column(the ones and twos)? and how can you 'realize' that right off the bat?

[@RoderickEtheria]

I'm not entirely certain my logic was not flawed there, but it was certain that there had to be a 1 and a 2 in each of the killer sudoku groups along the sides. I started to feel like they would result in a non-unique solution if 1 and 2 were located in the same 9x9 box , and started to feel like a 1 and a 2 would have to be placed in the center box in each of the two sides as I started to feel like those 2 boxes in the grid were like insertions into the column compared to the other squares in the same column. My logic might have been faulty, even though it led me to the correct solution. It didn't occur right off the bat, but my conclusion was reached quickly in one group, after realizing that a 1 and a 2 had to be in each of those groups in the corners of the grid, which is obvious, as the 1 and the 2 in the second and eighth columns had no other location where they could be placed in the first column, and each column contains all numbers from 1 to 9.

[@danpowell806]

@@RoderickEtheria I figured out that the 19 and 20's along the side had to all have both a 1 and 2 in them as soon as I did the mod-45 math, which led me to figure out what was in those cages.. incorrectly, as it turns out.

[@samb5017]

How come you can't compete?

[@richardrobertson3115]

I was wondering that as well.

[@CrackingTheCryptic]

Not enough time I'm afraid. The thought of having a whole hour and a half uninterrupted sounds like a completely mad dream to me!! Also, I'm not fast enough. I'm quite decent at logic but not at speed :(

[@haakonmusic7172]

@@CrackingTheCryptic Well you did this puzzle in a 23 minute video, while you commentated your thought process... seems pretty speedy to me? The time aspect is completely understandable, though

[@pizzapm]

This one took me 2:38:24, not good in the slightest but I'm very happy just to have completed it c:

[@Ardalambdion]

I seriously tried, but followed a bad lead. Didn't realise the 12 pairs were located at AI46 and gave up.

[@Ardalambdion]

Besides, if it is a real sudoku (with only 1 solution), why can many of the 1s and 2s switch places without consequences?

[@Epic-1224]

How is 56 seconds even humanly possible?

[@timothyjames2477]

At 18:20, why couldn't it be a 1?

[@glennmelven3414]

In that cage there is already a 1. Digits cannot repeat in cages according to the rules.

[@AnonyMats.]

Took me 1.5 hours, but got there eventually!

[@helenamcdonald5042]

Why were the two 1-2 X-wings linked?

[@sarsoar]

They shared cages. Cages cannot have repeats.

[@HeroDarkStorn]

I forgot, is a part of killer rules, that "boxes-with-sum" cannot contain duplicit numbers?

[@danpowell806]

Yes, numbers within a cage are unique within the cage.

[@richardmead9785]

Way too many keystrokes! Is the solver that cumbersome to use?

[@MubarkAlKhatlan]

that was hard.

[@MrOPD]

Why couldn't the 12 cage in c5 be a 3-9?

[@tallrapp]

Because the 16 cage at f5 can only be a 7-9, thus eliminating a 9 from the c5 cage possibilities

[@mozartdminor]

because the 16 cage in c5 had to be a 7/9 pair, using the 9 for the column

[@jacobclaassen4709]

Wow I messed up somewhere lmao

[@ScurvyDog2222]

As well it should have been. kzbin.info/www/bejne/h4OwZYdumdZspcU Put the 9 straight in! It was the only 9 possibility in the box due to the 12 pair below.

[@smsie192]

52:45 - hard indeed, but a beautiful puzzle. Somehow despite the difficulty it never managed to feel frustrating :)

[@gizel4376]

110 min, at least i finish it no mistake this time

[@LednacekZ]

Didnt find it very hard. sub 20 minutes. I have done a lot killer sudoku though. And without it being in competition.

[@jamesahibbard]

50 minutes 22sec for me.

[@MentalMadness58]

I waved off after 45 Minutes of trying by myself...but maybe there will be an easier one next time I am able to solve on my own.

[@anjubliss8029]

I was wondering - does anyone solve killer sudoku through memorization? I solve them all in my head (no writing down) - it does take a bit longer but I really enjoy the challenge in doing it this way.

[@lewiswegner2339]

this was gross... 1h 18m 5sec no help