I'm impressed. You solved that much more cleanly than a computer solver I threw the puzzle at after I got stuck. Score one for human intelligence over machine intelligence :-)

As Simon nowadays tries to avoid using uniqueness, here is my approach without it (at the moment he applies it, 23:35), I dont know if anyone said this before (it may seem like bifurcating but it went all inside mi head, it took me nearly half an hour of being stuck but i am happy now): - if r6c8 is 6, via r6c1,r9c1 and r9c2, one can see r1c2=5 - if r6c8 is 4, box 3 must place 4 in r1c9, and then 2 in r2c9, so r2c5=5 So, there is a 5 in either r1c2 or r2c5, so r1c5=2 because it sees both cells After that the puzzle can be done without using uniqueness :)

These techniques are easy to understand when you or someone else explains it But very Difficult to Spot.. at least for me. 👍🏻

I would love to see you solve some of the puzzles with eye tracking software which would make even those times when you are just looking at the board not saying anything really interesting.

@oswaldchangerton5328

5 жыл бұрын

I love this idea. It would also give more insight into his method of looking into what to do next.

@TheDarkalkymist

4 жыл бұрын

@@oswaldchangerton5328 it really depends on how individuals process the information, a large portion is related to pattern recognition and then applied processing

10:10 - 3 digit relationship chain 13:15 - empty rectangle 17:14 - x-wing 22:50 - uniqueness 24:40 - piece of logic

19:13. Been binge-watching ur channel lately and was reluctant to try this when you mentioned the “diabolical difficulty” but pretty happy with that time.

The "9-6" thing and the two 5s tripped me up for ages! I can't imagine I would have ever spotted them!!

Mark is like your tester for food poisening.

Needed the video, in particular the trick with the 17 square and then the empty rectangle, to solve. I was amazed Simon found them so early in the solve, relatively speaking, after the more obvious cells were filled yet before getting completely stuck. Amazing.

16:40 The empty rectangle on 6 and 9: I didn't spot it myself unfortunately, but it was another situation that I could analyze as a finned X-wing. The effect is the same: ruling out 6 and 9 from R3C7.

When you talked about the 7s at 11:20-ish I noticed a Skyscraper with 7s of row 4 and 6 which ended up resolving the 57 later on when you explained how you eliminated 6 and 9 from 5689 to get 58, something like that shape is genius to me, no idea how you could see it but I'll for sure trying to look for it more often.

a rare simon uniqueness deduction.

11:30 that moment when he pulled the nishio out. impressive logic.

i got stuck at 5:55 where he said there was going to be a terrible sting haha

Thanks, I learned about the "Empty Rectangle" :D I get stuck very often on these extreme sudoku's,,,, and i see the area of 3 squares where there have to be 2 numbers (6 and 9 here),, and I feel there has to be done smth with that, but couldn't work it out. Now finally i get exactly what to look for :D Thank you good man

23:00 - 23:50, you take advantage of "uniqueness". In your later videos, you say you don't like to do that. Looking at the puzzle at that point, is there a way to progress without using uniqueness? Oh, I see it now (thanks to watching numerous videos of yours the last few weeks): Rows 2 and 7 have an X-wing of 7s. So, r1c9 can have that fin (7) removed. That leaves a 2-4-5 triple in row 1. Which makes r1c3 a 1, and the puzzle is cracked.

@solfeinberg437

2 жыл бұрын

Not seeing a 2-4-5 in row 1, after removing the 7 in C9. If there wasn't the possibility of a 1 in row 1 column 8, okay.

Thank you for solving the puzzle! It was a lot more helpful than a computer solver

What a lovely video and a good classic Sudoku

I haven't been able to shift click multiple cells either, not sure if there was an update that removed that. Also, you don't need to double click on cells, a single click should suffice. I noticed the other day when you were doing the partial killer sudoku, that the highlighter doesn't show up in the yellow-color boxes. It's still working, you just can't see it because they are the exact same shade. Hope these notes help! Thank you very much for the content.

@ManiacalKiwi

5 жыл бұрын

Use ctrl instead.

@oswaldchangerton5328

5 жыл бұрын

@@ManiacalKiwi Thank you!

@anonamatron

5 жыл бұрын

What software is this? I'm interested in trying it but I don't know the name.

Great solve, wow... The uniqueness had me tumbling...

i love when he strikes a key and it just POPS!!!

I had got stuck up to the point where you had the 3 x 58s in a square wth 1568, I think. It's never occured to me to assume that '58' could then be removed from that corner because of not making it 'unsolvable' ('unique' rule?). I think this is what I have been missing in puzzles where I have got stuck before and I end up with two digits in four corners that could be either way round. After that assumption, the puzzle pretty much solved itself! Thanks for the videos anyhow, they've rekindled my interest!

Absolutely brilliant, thank you! Thank goodness for the "pause" button.

after watching a pro struggle to solve this one, i am feeling quite happy with my 40 minute time to solve

This was a tough one for me but you showed me the way out!

I put this puzzle into Hodoku and it rated it at 1706 (unfair)

I took about 2 hours to solve it, but I don't memorize many of the advanced tricks like skyscrapers or empty rectangles. I think that every one of the advanced tricks is equivalent to guessing a candidate and running into a contradiction.

What a great solve!

23m41s. Quite pleased about that, although I did have to rely upon Bowman's Bingo to crack the last chain (much to my chagrin).

"all that work" you did (quoted when you got a 9 from it) to see where the 6 and 9 went in the upper left corner forgotten, it would have solved a lot of problems during the rest of the solve if you had pencil marked in the 6 in r3, c2+c3.

@23:24 - if you had checked C3 at that point, you would have noticed it can only take 1/6, effectively giving you a hidden pair that immediately resolves B3 (5) and B7 (8)

@jawaharlalgupta9039

3 жыл бұрын

please explain in more dtails

Instead of using the chan for the 1 in box 5, I noticed that box 4 was the only one where 5 could go in row 5, so r4c3 couldn't be a 5. Now, the cell to the right of it was the only one where a 5 could go in that row.

When you are pondering the uniqueness problem at around 23 minutes in, you don't really have to. There is an empty rectangle in box 3 that will solve that leaving no risk of a deadly pattern.

I'm waiting for the "Second Circle of Sudoku Hell" puzzle. ;-)

Great job 👏 the game

Had to bifurcate 8s in central 3x3. Guessed wrong - looooong chain. Ok after that.

I solve very few of the puzzles on this channel entirely on my own, but I was able to solve this one. I feel as if I was lucky to make a mistake that turned out to be correct, because I am not at a level high enough to solve this based on how you described it.

Is the 10:10 three digit relationship called Sue De CoQ? It feels similar but i'm not sure, and this pattern is pretty hard to spot I suppose.

One of these days, the empty square will come to my head...

WOW! Could only do it with help in two places.

I will have to watch this once/month for a year to get this in my blood!

Denying cell H3 to be an eigth or a five just by the 'uniqeuness logic'-rule is not a rule I knew I was allowed to apply.

14:57 for me! not too shabby

35 minutes. I did have to bifurcate to get progress, but still a good solve for me

This one was the real deal!!

I play Samurai Sudoku (5 linked boxes) and I always start by placing in the most obvious numbers why don't you? For example the very first number was 3, row 4 column 8, it needed no other entry on the table to allocate that number. Can you have more than one solution for a sudoku because in the Samurai version I have found variable answers to the puzzle. The other query I have is do you believe extrapolation is a logical approach. I have done it but feel uncomfortable because I am acting on a hunch and then stretching out the results of that hunch.

Amazing video thanks

Good solve, that was way too hard for me.

Wasn't as bad as your title suggested. Took me about 25min - (did bifurcate - was so tempting with lots of pairs - why else is the undo button there? ;) )

@hhaavvvvii

5 жыл бұрын

To fix that time towards the end of the puzzle where he overwrote a number by mistake.

Ugh. I fell for it. My logic led me to placing a 7 in the erroneous 17 pair square that can't ever be a seven and must be a 1. The caused the 67 pair it was looking at in Column 1 to be a 6, which is actually true, but it led me to check the solution up to placing the 7 and the software said "looking good" even though it broke other things. This is when I realized that the checker is not checking against the actual solution. It is only checking if you have a valid Sudoku at the end of the solve, not if you have the solution to the particular Sudoku at hand. If John and Simon verify each puzzle has a unique solution before they use it to make a video, that's not a problem,, but you could enter anything valid except for the empty squares and you'd think you only need to fill in the rest of the empty squares correctly to finish. Not at all, because I assume they DO verify uniqueness and you'd get stuck continuing down an invalid path without knowing it.

Fantastic solving. Solving live in such a short time is really great. Doubt if I would have spotted anything useful from that empty rectangle involving 6 and 9. I have watched some of your videos and this is the only time I have seen you eliminate one of the values by proving the other value does not work. I mean R6C4 had a possible 17 set and by picking 7 there it lead to a conflict and hence you put 1 in R6C4.

@ 23:04 I agree (5/8) is not possible, but why would 5, ... or 8 not be possible?

@hiawathadevries7222

3 жыл бұрын

Is this the right deduction from this uniqueness?

Wow so many brillant deductions compared to my solve

My question is: Around 11 mins in, when you figure out the trick for row 6 column 4, if this is not just a form of bifurcation, can you answer please if there is a name for the logical strategy used? I am becoming seriously addicted to this channel, and am improving my sudoku logic by leaps and bounds. I keep coming back to this one - and many others - until I can solve them without having the trick memorized... Thank you!

@lsmart

3 жыл бұрын

Simon just noticed the link between those cells, but did not seem to use any known method. It is not bifurcation, however, which is simply guessing an option and following through until you get stuck. Here, he demonstrates why one solution can logically be eliminated; it is no different than x-wings or y-wings.

28 minutes, I'm actually proud of the result

23:54 I like those considerations of unicity of the solutions... However the first time I used it, it went wrong, the puzzle was computer-made with no unicity check. But anyways great great advice!!!

@viktiger

3 жыл бұрын

I'm not a fan of bifurcation, and i'm wondering if there was an alternate approach at that point? Simon?

@eternalblasphemy6526

3 жыл бұрын

@@viktiger There is an alternate approach to the puzzle. ^ could never go r6 c7 and 8 because it woudl force 6 in both r5c3 and r2/r3 c3 which would clash together. This means: the only place a6 could go in box6 is r5c7.

Didn't spot the empty rectangle. Actually had quite a few more digits in when I hit the wall and having watched to that part of the video and eliminating the 69 from r3c7 the puzzle just fell apart where I'd done all the other work.

23:22 In later videos you don't like using uniqueness. So I tried to find another logic here. First I filled out the possible 6s and 7s in box 1, which leads to removing a 6 from r3c8 and removing a 7 from r1c9, Then I noticed that the 56-pair in r5c3 connects the horizontal dependencies in rows 1-3 with the vertical dependencies in columns 7-9. And there it was. Putting a 6 into r5c3 lead to a failure. It will not allow a 1 in column 8. Ergo, r5c3 must be a 5 and from there you can solve box 1 and box 5 and the rest is pretty much cake.

@igoretski

3 жыл бұрын

Thinking like Simon, I wondered how this could be found easier, with an X-Wing, Skyscraper, Swordfish, Empty Rectangle. But no matter how I tried, it didn't solve with one of these patterns, as far as I can see. Except maybe you can notice like an X-Wing between boxes. When you find that rows 1-3 and rows 7-9 can not be restricted further than 2 options, you have to look at boxes 4,5,7 and 8, how they interact. You immediately see that boxes 7,8 have no influence on columns 7-9. And box 5 has no influence on rows 1-3. So the only place that has influence on rows 1-3 AND columns 7-9 is in box 4. And then it's obvious it must be r5c3 that radiates both to rows 1-3 and columns 7-9. By the way, the same logic from the other side around could only be found by noticing that a 4 in r1c8 leads to a conflict in r5c3.

@eternalblasphemy6526

3 жыл бұрын

I 'vehad the similar logic path but vice versa. Look at box 6: 6 has 3 placement (r5c7 and r6c7 and r6c8) in box 6. The funny thing is, if the 6 goes in any of two places in r6 in box 6, it will break the puzzle, az it will force 6 twice in c3 (one in box 4 in r5 c3, two in either r2c3 or r3c3 in box 1). Hence, the only palce 6 could go in box 6 is r5c7.

32:58. That was a pain in the butt

At around 19:58 you had the opportunity to get the 8 as sudoku limits the x-wing with the 58 in the last cell where you have the corners 1-8. Neither a 5 or 8 could ever exist there as the sudoku would break allowing multiple solutions. Would that be an accurate observation? Thanks

@karactur

4 жыл бұрын

Oops you then explained that point at 23:36! Lol

I didnt quite get how he removed the 5&8 from r3c8. He called it the uniqueness rule...how does he know that the 5&8 will end up in a result that is "a solve" but because of inverting the numbers its not a unique solution and therefore doesnt count. I fail to see how he is sure of that fact? Can anyone elaborate?

@StonerBill420

4 жыл бұрын

One unwritten rule of creating sudoku puzzles is that the puzzle must have only one solution... so if you end up with a situation where you can place either number in the box and solve it, it is not considered unique since it has multiple solutions

Sorry for the stupid question, but at 19:24, do you know that r4c7 is a 9 because r4c3,4,5 are a triple which eliminates the 8 from r4c2? New to these harder puzzles.

@igoretski

3 жыл бұрын

Sorry for the late answer. In row 4 the 9 can only go in columns 3 or 7, because in column 2 you have the 28-pair, the other numbers are set, and there is alread a 9 in the middle box. So when he sets the 9 in r2c3, he immediately knows where the 9 in row 4 goes.

At 23:50, r3c7 is reduced to a 1-6 pair. In box one, r3c2&3 have to contain a 6 and r1c2&3 have to contain a 7. Therefore, r3c7 is forced to be a 1. From there everything else quickly falls into place. Great job on solving and a beautiful puzzle. I usually solve until I get stuck then watch the video to get the missing bit, puase the video and continue on until I finish or get stuck again.

@lsmart

3 жыл бұрын

Alternatively, r3c3 is also a 1-6, so the 5-6 in r3c2 must be a 5, which solves everything quickly.

took me 40 minutes quite proud

any way to finish without using the uniqueness assumption at the end?

This one really made me miss my printer. A total pain on the computer, but I snuck in under an hour, so I'll be content.

Watching now at 21:54 (Yes, I got a bit behind...) This is looking like a BUG. I love the BUG. (Edit: It wasn't a BUG... Sad panda...)

@snjyjn

4 жыл бұрын

You can take a different solution path and get it to the BUG! 31 squares, 29 of them with 2 values, and 2 with 3 values in them.

23:05 Can anyone see logic before the uniqueness? There is somewhat complex logic chain, but I cannot see any "rule" to use to continue. Here is the best I could get: - 6 in r1c6 forces 6 into r3c2/3, which makes r3c8 1-5-8. - Assume 5/8 in r3c8 => r3c7/8 form 5/8 pair - r2c8 is now naked 6, r6c8 4, r6c6 7, r4c4 5, r4c3 7, r1c3 1 - the last 1 eliminates 1 from r1c8, and there is no place for 1 in box3, contradiction with no 1 in r3c8.

@iamisaid2295

4 жыл бұрын

yes I also didn't quite like the "this is a good puzzle therefore it wouldn't have this 5-8 X wing here". That was opinion, also at that stage I had only a 1,8 in that box, due to ruling out the 6, and I'm not sure why I didn't have a 5 there. This "logic" isn't obvious. i'm following you until your r4c4, i get a 7 there. I really don't like solving sudoku by doing this "what if x10hypotheticals"

@TheBurntan

4 жыл бұрын

What is logic at 24:22 to eleminate the 8 in r3c8 ?

@HeroDarkStorn

4 жыл бұрын

@@TheBurntan he literally says he's using uniqueness, that is if there was 8, there would be 2 solutions to the puzzle (switch 5/8 in the two pairs). Also, I never noticed back in the day how bad the sound was on these videos, what a trip on a necro-ed comment :D

I'm very bad at Sudokus . This one I've find it beautiful but no much difficult.

Use what is called Gordon’s rectangle when you get 2 numbers on the corners...you can eliminate those 2 numbers from the other corner....with the explanation that it is impossible.....because it would create 2 possible solutions and machine puzzles can never have 2 solutions...jim sheehan

Took an hour for me before I finally caved in and had to bifurcate the final string.

15:50

"Off the scale difficulty"? This puzzle has a lot of naked and hidden doubles and triples, but doesn't require any advanced techniques to solve. Stiil, it was nice to see the chaining example.

@lsmart

3 жыл бұрын

Well, perhaps you solved it differently, but Simon used a uniqueness argument, a totally unobvious and contorted argument using empty rectangle, and a completely original argument involving three linked set of cells over two grids. I'd rate that quite difficult.

I don't fully understand the uniqueness you used. I get why r3c8 can't be a 5 to make the 58 pairs but why can't it still be an 8

@eternalblasphemy6526

4 жыл бұрын

Forget the rule, just pay attention to the r3 c3. It allows only 1 and 6 which would make a 16 double pair and 56 and 58 which would be resolvable.

Have you considered switching to using Hodoku? It would be easier and more efficient to use (especially for all the pencil marks you manually enter - seeing all of your extra/duplicate pencil marks are distracting :-S...)

@glennmelven3414

5 жыл бұрын

He actually needs and uses both types of notation for different purposes. Going with the style that Hodoku uses would not allow him to do that.

@ChessRabbitt

5 жыл бұрын

Look at some of the older vids. They use to use that very software.

@ChessRabbitt

5 жыл бұрын

Look at some of the older vids. They use to use that very software.

You lost me @ the 12 min mark. I still can't see how you got that 1

Was I the only one that was staring at the triple in c6?

Can anyone suggest an android app for classic sudoku? I have been using one by "Beetles Games Studio" and they feel very hard sometimes.

@Kraidoz

5 жыл бұрын

I like the way it has the option to highlight all numbers that you select... but the hint option straight up fills in a blank space meaning I learn nothing!

@glennmelven3414

5 жыл бұрын

You should check out Hodoku. It even has a training app.

Where can i obtain this software? *i guess i can keep using crayons ☺

Sory, had to guess at 1 point..

You solved the puzzle without explaining how you go about, your thought process. I understand that this lesson is for expert level. Maybe, you could put the Level at the title, so people like me, an experienced beginner might stay off. Something like beginners, medium and expert. Great lesson nevertheless. Keep up the good job. Thanks. Cheers.

@trdi

4 жыл бұрын

I don't think you are an experienced beginner if you couldn't follow. He explained every single step.

@selueen3028

4 жыл бұрын

If there's "hell", "diabolical", "fiendish", etc in the title, it's guaranteed to be expert level puzzle. Demonic words are reserved for hardest tier puzzles in sudoku world.

@davidh.4944

4 жыл бұрын

@@selueen3028 Another clue for me is the running time of the video. If it takes the experts more than 20 minutes, I know it'll probably take me at least a couple of hours, if I can do it at all.

This one pissed me off, tbh. Spent so long on a guess just to get the very last number breaking the puzzle. I'm out.

Solved in 13 minutes and 33 seconds using only logic and basic Sudoku techniques.

1 hr 31 minutes myself and I had to bifurcate two or three times.

my first thought wasn't 'This'll be fun...'

It took me 1:18, yes the key was in square 4

i knew it. there was just something fishy about 69.

45 minutes Edit: That moment I'm watching the video and there is a whole confusion in Box 9. 5-8 pair bottom line, 6 only in the middle line because there is and 8 in the line. Had to stop the video for a moment here.

took me about 45 minutes or so. im just a novice though so ill take it lol.

Practically impossible to follow due to the huge number of disturbances from annoying and irrelevant adverts.

I love your channel, but your clicky-clacky keyboard on this one, right next to the microphone, is driving me crazy.

Sorry, but for me uniqueness is a form of cheating.

@benjikat1

5 жыл бұрын

What!? As far as I'm concerned it's as much a given as "there is 1-9 in each row" etc

@M4ke4l

5 жыл бұрын

It's not a cheat, a sudoku is supposed to have a unique answer, so it's a technique used to avoid breaking the rule of a sudoku like any other technique.

@glennmelven3414

5 жыл бұрын

Using uniqueness is just another logic tool. What is logical about a puzzle having a solution that requires there be no solution?

@mhelvens

5 жыл бұрын

I kind of get it? If not cheating, it's like making an educated guess. I've never seen the rules of a sudoku guarantee that it has a unique solution (as opposed to multiple valid solutions). It just so happens that the good ones do, in order to make them solvable by pure logic.

@jurgenkloppshead8373

5 жыл бұрын

having those pesky starting numbers in the grid is cheating too

This is what my notation is like on medium 🥲