The Sudoku You Should Not Enjoy Solving
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- čas přidán 28. 05. 2024
- Today's puzzle was published 23 hours ago! So this is a sort of bonus, exploring some of the channel's background, and trying to explain why we prefer handmade puzzles to computer-generated sudoku. The puzzle Mark tries is available at app.crackingthecryptic.com/su...
Normal sudoku rules apply.
The version of the puzzle that Mark solves is missing two given 4s that appear in the correct version above, and therefore the version he is attempting actually DOES have two solutions! However, the ‘solve path’ is basically exactly the same!
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▶ Contents ◀
0:00 Theme Music & a chat about what the channel and this video are all about
7:50 Start Of Solve - Let's Get Cracking! - Zábava
LOL @3:04 "There is never an alternate solution to one of our puzzles. We only publish puzzles which have only one solution." @3:10 with a big magenta background, "Except this one." I had to take a break to stop laughing.
Fun fact: any 9x9 classic sudoku needs to have at least eight unique given digits. We could have looked at Mark's original grid, seen that there were no 4s or 8s, and immediately known that it was not unique
I did not know that. Is there a source document or link showing how this was figured out?
@@SmartHobbies I don't know of any published works explaining this, but it is relatively simple to understand once you consider the framework of solving sudoku. Think about the two ways you can place digits in a classic sudoku. You either have a hidden single, where the presence of other digits x only allow x to go in one cell in a house (row/column/box), or you have a naked single, where every digit except x is pointing at a cell, forcing that cell to be x. If you think about it, any other logical step you might take, like wings, pairs, triples, etc. is just a more complex form of one of these two categories. Some variant rule sets have other ways to place digits, such as mathematical requirements, so this rule is only absolute for classics.
Given these two categories, imagine a sudoku grid that has all the 1s, 2s, 3s, 4s, 5s, 6s, and 7s filled in, but there are no 8s or 9s. You cannot place a digit with a hidden single, because you need other identical digits to narrow down the possibilities. You cannot place a digit with a naked single, because every blank cell still has two possibilities. The puzzle is not unique, because if you arbitrarily choose one configuration for the 8s and the other for the 9s, you can just as easily switch the positions and have an equally valid solution. If, however, you had a given 8 somewhere, then that may be enough to disambiguate the 8s and 9s. Depending on the configuration of the grid and the remaining blank cells, it could require more than one given, which is why I say "may". Now, you don't need to have any given 9s in this scenario, because once you have enough given 8s to place the rest with hidden singles, you can also place the 9s with naked singles.
And if you were curious, this same logic applies to any regular sudoku with size n, where you need at least n-1 unique given digits. You may find it interesting to play around with 4x4 grids, which don't take long to solve, but are big enough to illustrate this phenomenon. Just start plotting random given digits, try to solve the puzzle, then delete it all and repeat.
@SmartHobbies if there are two digits that are completely missing from the grid (say x and y), then any valid solution would have a twin solution with x's and y's swapped round. After all there is no arithmetic meaning to the numbers in a classic sudoku, they are just 9 different symbols that you could swap for letters or colours or emojis or whatever you want.
@@ianhill5373 Thank you. I never thought about that until I saw that comment. Do you create Sudoku puzzles?
Great bonus video! Not only it was a comprehensive introduction for newer viewers on solving stratagies, jargon and scanning, it was very amusing to watch as a long time subscriber because of the irony of fate 😂
I don’t mind doing computer-generated classic sudokus (I solve the NYT sudokus most days). But my biggest problem with most of them is that the software doesn’t give you the notation flexibility that the CTC software does. So I have to choose between pencil marks being digits in a box vs. cell candidates, and can’t really distinguish between them. That slows down my solve quite a bit.
If you google for "Sudoku Exchange bookmarklets" you'll find a tool that allows you to open the NYC puzzle on an alternate site that does allow dual notation.
About 15 minutes for me and there was nothing fancier than xy pairs and triples. Really quite straightforward.
Brilliant video, Mark.
As much as the 2x solutions wasn’t an ideal ending, the explanation as to the differences between computer-generated vs ‘handmade’ puzzles, plus the guidance re x-wings, y-wings and the different methods of marking, was incredibly insightful.
Perhaps slightly basic to the seasoned sudoku veterans, but a real gem for any newbies to the channel (like me)!
Thanks again, and a great watch as always.
Great explanations. I think it was the Y-wing which was the difficulty for this one. Glad you went over the y-wing too as it makes more sense to me now.
I fully understand y-wings, and have done for a year or two following a couple of good videos on this channel a while back that explained them. Still doesn't mean that I can ever spot them in the wild though 😢
@@stevieinselby Likewise! They make perfect sense to me, but I think I'm correct in saying that I've never noticed one myself.
@@stevieinselby I think it goes back to the "guessing" routine. The y-wing would be a "simple" guess of only 2-3 moves. Where the 2 numbered cell (let's call it the Pivot cell) forces a block of a different number in another cell. This is created by 2 "blocker" cells. The 2 blocker cells must be within the same Block, Row, or Column as the Pivot cell. The 2 blocker cells would contain the number in the "target" cell that would be blocked. So there are a total of 4 cells affected. 1 pivot cell, 2 blocker cells, and 1 target cell.
They do look like they are tough to find and you would only find it while in "guessing mode". I imagine, while guessing, to review all cells with 2 digits. Then see if there are other 2 digits cells within the Block, Row, or Column with similar digits. Then look if there is a target cell.
Mark: your shouldn't enjoy this
Also Mark: wait, that's kinda clever
If the point was to show a sudoku that wasn't fun to solve, you made the point. I much prefer hand-generated sudokus with interesting solve paths.
For whatever reason, I found this one to be much more fun than typical computer-generated puzzles. 🤔
This is great. A classic Sudoku. I always love it when Mark comes back to the basics.
I enjoyed this... delightful to find Mark explaining his way out at the end.
I finished in 14:28 minutes. This is why I don't usually do regular Sudokus anymore. I usually end up having to bifurcate the end and that makes the ending unsatisfying and frustrating. The thing I really like about variant Sudokus are the unique logic and many ways to get to that logic, by either using the internal logic of the puzzle (German Whispers never have 5s, Black Kropki dots can never have 5, 7, or 9, etc.), the external logic of the puzzle (Math, The Secret, Phistomefel's Ring, etc.), and Setter's Logic (SET Theory, Why would certain clues be placed, Previous Puzzles with similar logic, etc.). This gives a lowly skilled solver like me the opportunity to try a different method if I get stuck on some parts.
I never tire of hearing you or Simon tell about the origins of this channel, or talk about each other's solving techniques or location ("Mrs. Rochester" made me laugh). And you took the time to demonstrate and explain Snyder notation, which was a huge eye-opener to me when I first started watching the channel. The fact that you also were able to show an x-wing and a y-wing (and that you explained each so well) was a huge bonus. And of course there was the humor of the puzzle actually not having a unique solution as you were working on it! I loved this video - thanks for this "bonus," Mark.
Straight forward puzzle. -- But then I had the advantage of the 4's! I also have the advantage of a few years of CtC training !! 😀
Straight forward to me because when I got stuck at the end I bifurcated and guessed correctly on the first try 😆
I read CtC as "CQC" and though of Metal Gear😢
Even with the 4s on, it absolutely isn't straightforward. The end requires either bifurcation or some bizarre advanced techinque that I'm not aware of even after watching CtC for 3 years.
@@istvanmagi473 Sorry to hear that. I used simple basic techniques such as pointing pairs found using Snyder notation. Never had to guess anything. I'm no genius, and many's the time I've had to watch a video of the solve of a puzzle only to find I missed something really simply like a hidden triple staring me in the face!
loved how you explained the different techniques throughout the solve! thanks for teaching!
That was a really nice explanation of Y-Wings! As a huge novice, thank you for showing me :)
Well, I found that pretty straight forward, now to watch Mark's solve.
Ps, my favourite setter is Clover. I love how her puzzles unfold, like a carefully wrapped present.
colour strategy is absurdly brilliant!
Oh the irony! Thanks for the entertaining bonus video Mark!
I had no idea there was a world sudoku championship, let alone being hosted in Canada (and I checked out where and it's only about 6 hrs away!) Very cool! I wonder if you can spectate?
Thanks for doing this one Mark! Every now and then I get stuck on a computer generated sudoku and I'm always wondering how you would solve it (but I have never sent an email asking 😅).
This was actually fun, and I'd suggest you add one of these examples once in a while...
Cheers
Yeah I have to agree about hard puzzles when made by a computer, you get to the end where you have to do insane logic like xyz wings which feels like guessing or something like BUG+1. The beginning you can solve most of it by asking where does the x goes then go through the numbers a few times before you need any harder logic. For this on when I got stuck at the end and not completely pencil marking I looked at r5c9 and used BUG and the puzzle fell apart. It probably the wrong situation to used BUG, but plugging in one of the digits that it was limited to two choices then following that logic can suck.
Honestly I wouldn't regard XYZ-wings as particularly insane logic. It's more the long X/XY-chains that I think are people deceiving themselves into believing they are doing something other than bifurcation.
Thank you so much for the bonus puzzle!! Hope you’re having a great holiday! Also enjoyed watching the opening explanations! ❤❤
You are wonderful Mark.
ahhhh - as a new viewer, I very much appreciate the introduction and explanation -- many thanks
I think that computer generated sudoku do have a role when you first start solving sudoku, but when you get into it, you quickly notice that the logic used on these computer ones never really varies. However I loved todays puzzle taking us back to basics!!
I'm definitely guilty of over pencil marking. I'm slowly getting the hang of Snyder notation.
Absolutely loved the history lesson sbout your channel. I've been watching for years and learned something new.
God you're a BEAST, Mark!! I love watching Simon waltz through puzzles with elegant logic, but I also love watching Simon bulldoze like a boss!!
13.05. First time I have beaten Mark's time by any significant amount although having the given 4's does help!!
Beautiful puzzle.
This was a hilarious disaster of a video, and my first Mark video! Great work!
Thankss for the solve. It is not often that you see colouring and it is technique I use frequently I must admit I do like your method of colouring - I learnt something . For me the solution fell out with conflicting 6's in R2,C3 which then ended up dropping out a 48 pair in R2, leading to a 35,36,35 groupng in R2 - giving the 6 in R2C6.
24:49@#1533. I for one, enjoyed this one. Most of the solve flowed very smoothly, right up to a final deadlock. But from experience I know that that point is where you can often find y-wings and empty rectangles. I used the latter on 8s to break through and finish it off. I would've achieved a better time, however, if I had started with that digit instead of walking numerically up through the remaining candidates.
Where was the "Empty Rectangle?"
(I just mentioned that yesterday or something - and the other person didn't answer , or didn't know)
Where was that Empty Rectangle though?
(Someone else said "swordfish on 8s," so maybe you meant that?)
You spotted an Empty Rectangle though?
Where?
Thanks
@@stevesebzda570 I don't remember exactly now, but it was the same elimination Mark made with the y-wing about halfway through his solve. If that cell contained an 8, it would have chained around through a pair of cells lower down, and made it impossible to place an 8 in box 3.
Very often these patterns overlap, and the swordfish, ER, and y-wing are just three different ways to spot the same conflict. I personally find ERs to be the easiest to find, so I always look for them first.
@davidh.4944 I couldn't find it (the ER cell ).
You said it was similar to the y-wing mark did in the middle of the solve.
(An 8 somewhere chained down below preventing an 8 being in box3)
Is the ER cell in box2 maybe?
(An 8 somewhere in there would prevent an 8 in box3?)
Box2 maybe?
@davidh.4944
I can't find it.
Thanks anyway.
Box2 though?
Great video once again!
That was amusing, after categorically stating that you never do puzzles with more than one solution. Actually, there was one puzzle on the channel which explicitly had two solutions, but I can't recall the details.
You could spot the problem with that 38 cell by considering C6. It's effectively the same problem, but attacking it from the opposite direction. Had you transcribed the puzzle correctly, I don't believe the solve would have gone any differently, other than not ending up with a deadly pattern.
It actually wasn't a bad puzzle up to the point it needed brute-forcing. The y-wing was perfectly acceptable, and if anything it improved the puzzle. I'm sure a human setter could have tweaked it slightly to have a more satisfying conclusion.
Same technic for me as needed to colour 4s and 8s as well
7:47 for me. This was all straightforward sudoku, no fancy Y-wings or chains or anything like that that other people are commenting. Now I'm worried I messed up somewhere and got the solution by accident!
Exactly! I finished in just over 10 minutes, watching football and not paying full attention. Pencil marked the hell out of it but it all seemed reasonably straightforward.
Really fun puzzle to solve. =)
I actually had some fun logic-ing this one out. Took me a long time because I'm inexperienced with such sudoku, but I've seen enough CTC to have a clue what to do.
So, I'm kinda pleased I could solve it on my own - however, I absolutely *needed* the colouring tool. Getting this in an app without the colouring feature would have been pure frustration.
Jokes on you, I had fun solving this puzzle
17:05 for me with a couple of interruptions from the kids. Missed the Y-wing, but got the solution by figuring out that r8c7 always was an 8. Not sure if that technique had a name or not, but happy to have found it!
I'm curious how you got that; I'm at that point (just found the y wing) and I don't see how to eliminate that cell being a 9.
wait mark i want to volunteer at the sudoku championships if i don’t have too much school work. would you ever consider a “meet and greet” i want a selfie 🙏🙏
great video
Let's Get Cracking: 07:50
And how about this video's Simarkisms?!
Pencil Mark/mark: 7x (08:18, 08:23, 12:05, 12:14, 12:24, 12:43, 13:36)
Ah: 4x (12:35, 13:14, 18:05, 22:35)
Sorry: 3x (11:11, 15:35, 28:01)
In Fact: 3x (15:35, 15:58, 17:57)
Stuck: 2x (14:36, 16:06)
Brilliant: 2x (06:23, 07:33)
Break the Puzzle: 2x (21:36, 21:52)
Elegant: 2x (05:23, 06:16)
Shouting: 2x (12:01, 25:45)
Goodness: 1x (19:24)
Apologies: 1x (00:20)
Missing Something: 1x (14:49)
Hang On: 1x (18:05)
Obviously: 1x (16:29)
Progress: 1x (12:46)
Most popular number(>9), digit and colour this video:
Forty Eight (5 mentions)
One (38 mentions)
Purple (37 mentions)
Antithesis Battles:
Even (2) - Odd (1)
Row (13) - Column (10)
FAQ:
Q1: You missed something!
A1: That could very well be the case! Human speech can be hard to understand for computers like me! Point out the ones that I missed and maybe I'll learn!
Q2: Can you do this for another channel?
A2: I've been thinking about that and wrote some code to make that possible. Let me know which channel you think would be a good fit!
I think you were too critical of this puzzle. I got stuck so watched the start of your video and so then bifurcated to a solve. I then watched the end of your video and realised I had missed the Y wing (which I find hard to spot), which is the key to the solution. Overall I did enjoy solving it!
10:01.
I completely agree this was nothing like the usual fare here. Just a case of bashing the numbers in.
So appreciative of the care and thought that goes into the crafted pieces usually showcased here.
The Song of the Serpent earlier as an exceptional example of why those puzzles are thousands of times more fun than the generic computer puzzles.
27:45 You just need to know where one of the missing 4's is located. The second one is redundant.
24:45 - Guessing a 4
Looks like I guessed the 4 and 8 s in the correct positions !!!
7:52 for me; nice one!
That was more fun than expected. I do agree that computer generated puzzles are generally boring and a hard slog. But this one had x-wings and y-wings and no long bifurcation chains. Glad you corrected your mistake of solving a puzzle with two solutions and put up the correct version with a unique solution.
Very instructive!
Since without the specified 4s you were able to reduce the puzzle to nine 4-8 doublets, does this imply that only one specified 4 or 8 in any position would guarantee a unique solution?
If so, does the 2nd specified 4 make the puzzle 'overspecified' and guarantee either no solution or multiple solution paths?
No; if you have a puzzle with one solution and one solution path, then whichever digit would be found first you can add as a clue without changing that surely?
On the other hand it's almost impossible for a classic sudiku not to have multiple solution paths, there's just so many techniques.
Technically it wasn't a puzzle with two possible solutions... as it was mistranscribed. Not the puzzle's fault really. Still fun watching it. I like to see normal sudoku's once in a while. Good explanations for techniques too.
Actually simon did a puzzle where it had 2 solutions and it was actually in the rules. lol Simon was supposed to get it down to where it's all solved except the deadly pattern. Personally I didn't care for that one.
The thing about computer generated sudoku apps, is they have a solution in mind. So if you get to a place where you have 9 pairs of the same two digits you can still technically solve it. They just count your placement of ambiguous digits as a mistake if it's wrong, and you're only allowed 3 mistakes.
Got it in 10:09
The puzzle was straightforward and i actually did find it to be enjoyable. Don’t see what’s the issue
Now watching the video. I think i got is faster because i did not do coloring at all. No advanced techniques were mandatory here. It was all simple sudoku
Slightly harsh description of Simon as "Mrs Rochester", who was the mad woman in the attic!
26:26 Would have probably been quicker if I had bifurcated earlier. Totally agree that computer generated puzzles are much less fun than the regular fare.
I was SURE there must be a Y wing somewhere, but I just couldn’t begin to find it. I don’t know how you picked that out so easily haha
22:48 for me. After I read the video description, I tried to do as much as I could without using the 4s, so I could get as close to the video (in my head) as possible.
This was a fun video. I enjoyed the irony.
17:18 for me - I had to bifurcate at the end.
I didn't spot the Y-wing but even still I would have never been able to look ahead so many steps in column 6 to find that solve, even with the two given 4's.
Never realized my method of Sudoku was the Storm Trooper method. LOL
Finished in 17:45, and I had to trial and error the final logic chain, so you were right, I DIDN'T enjoy solving it.
World Sudoku championships will be 6 hours away from my home but l'll be in Asia. Classic me 😂
I enjoyed solving this one - mainly because I did.
at 22:45 you say you don't like this solution because "it is a kind of look-ahead" but you guys do that in almost every single "hand crafted" sudoku puzzle that you solve on this channel. It just seems like you guys would call the exact same solve "gorgeous" in a puzzle made by clover or jay dyer or fistomefel or aad, but it's icky if its not made by them for some reason.
I managed to do it in 18:50 but with error/pencilmark checks and lucky bifurcation as I'm still just a newbie 😅
Thanks for explaining. I was wondering what bifurcation was.
I'm curious to hear what's the easiest logical way to solve the final stage of this puzzle. @windchwang mentioned a swordfish on 8s which took me quite a while to spot in rows 2, 3, 5 and columns 3, 5, 9. Anything simpler?
Is that a swordfish on 8s?r4c9 is also possible in those columns, and r3c1 in those rows, no?
I'm not going to claim my way was simple, but this is what I eventually used:
The 56 pair in c4.
If r3c4 is a 6 it makes r4c1 an 8 which forces purple to be 4 in box 4.
However, if r7c4 is a 6 it makes r7c6 a 4 which makes green be 8 in box 5. Either way, purple is 4 and green is 8.
(It's really quite a long chain - I just chose to view it in two directions from the centre, to kid myself I was using shorter chains 🙂).
Edit: That was on my solve that had the given 4s.
Edit 2: Fixed a couple of cell references. (Thanks @psioniC_MS!)
@@RichSmith77 nice one! i think in your first case you mean r3c4 for the first position of the 6, and then r3c1 becomes an 8, forcing r4c2 to be purple.
i'm not sure if what i found is called a "swordfish", but if you take all rows and columns where 8 only has 2 possible positions (5 in total), then you are left with 3 8s to place, but the only possible cells are r2c3, r2c5, r2c9, r3c3, r3c5, r5c3, r5c5, r5c9 (the intersections of rows 2, 3, 5 and columns 3, 5, 9 without r3c9). this rules out 8's from r3c1 and r4c9. I hope this logic is sound.
@@psioniC_MS Thanks! I did indeed mess up my cell references. Sorry about that. You did well to decipher my meaning.
I don't believe your logic on 8s holds up. I cannot see why the following wouldn't be a permitted distribution of all the 8s at this stage: Going column by column from 1 to 9, 8s could be placed in rows 3-7-5-9-2-6-8-1-4. This has an 8 in both r3c1 and r4c9.
@@RichSmith77 I guess I overlooked that possibility. I must have thought some cells aligned in a certain grid fashion, but one pair did actually not.
@@psioniC_MS I replied to @windchang's original swordfish comment looking for further info. If there is one, it may come after further alternative progress. I don't see it emerge in Mark's or my solve paths.
At some point this puzzle needed a bit of brute forcing, which is not a strategy I like to use.
I had to color and bifurcate to get the solution, but I spotted that Ywing and that made me happy
I hate puzzles where I have to bifurcate, so I appreciate the channel so much! Thank you Mark for the amazing job you and Simon have been doing these past few years!
Fairly easy if you know how to color.
Completed in 7m01s
I think it's still fine to claim the *valid* puzzles you solve always have only one solution.
00:16:34
Click bate - but I'm sucked in! And dang it, but I plan to enjoy this puzzle.
12:21!! :D
20:31 for me, no bifurcation. I agree, not the fun solve. I'm very glad that you usually use hand-crafted puzzles. This helps me remember why I appreciate the sudoku setters so much!! I have not seen the video solve yet, so don't know how Mark solved it, but I used a few finned X-wings, and a couple XY chains (at least that's what I've heard them called). Very tedious!
16:50 for me
So, this would be the second puzzle published that has had two solitions. Anyone else remember the Hydra Sudoku? It had a unique placement of digits, but two possible snake paths.
czcams.com/video/xMO8_WN7v5g/video.htmlsi=Mx15MRAZXUJLH0zX
I think that this is good puzzle to demonstrate the coloring technique. I don’t think that it can be solved otherwise.
So Mark predicted that it would be solved by guess work, turned out not to be so with color.
@@stephenmccarthy1795He still guessed whether r8c6 could be purple, and then discovered a reason it broke.
18:52 for me.
I solved it
I appreciated this video, not only its irony, but Mark's validation of not liking what I call "if/then" logic strings. Oh, and the coloring is very nice!
I was slow and took me 29:03 to finish.
13:39 for me
Used the 4-less version... then coloured 468 triples... resolved uniquely once the colour of the 6 deduced.
Enjoyed both the video and the solve. I always solve the puzzle first to earn my shouting rights, so i didn't know it was computer-generated. Wasn't that bad. Not a worst case scenario.
21:24, I had to guess at the final numbers, gonna watch the video to see the logic that I missed (and the HARDER solve!).
35:25 for me @#2110
I think you're a bit unfair on this puzzle and in particular the criticism of the chain you used beginning in box 8. You had to notice that 48 pairs were showing up all over the place, you chose to colour them, you had an inkling about how picking one or the other would lead to a contradiction. I appreciate it's not sophisticated solving or a very smart trick, but it's not unreasonable to think that a human could, and would, as you did, work it out. I enjoyed this puzzle and I enjoyed the point at which I did something similar.
I made the guess in the 468 triple in column 9 that I thought would have the biggest effect on the rest of the puzzle and most likely lead to a contradiction, and it did, which gave me the digits I needed to reach the solution. Yes, it's bifurcation, but I think the better your reasoning for making the guess, the clearer your expectations of what it'll show you, the more defensible it is, and it was fun to follow the chain of logic around the grid until the contradiction I expected to see materialised. It showed me I was right to expect it and that was satisfying.
9:33 and nary a color required. This seemed like a very straightforward sudoku. But the, the fours were with me.
As the video started, I started mentally solving the puzzle on screen and quickly noticed there were neither 4s nor 8s in the grid -- which of course means it's not uniquely solvable as presented. I was quite reassured when we finally got to the card explaining the transcription error! An instructive video, even for a relatively experienced solver. I have nothing against computer-generated puzzles, and do the ones in my newspapers regularly, but they're the sudoku equivalent of cheap boxed red wine as opposed to a decent vintage bottle, of a fast-food burger as opposed to a steak, of over-sweet commercial cookies as opposed to what I'd bake myself. Better is better! 😼
I’ve found that a lot of the ‘difficult’ computer generated puzzles rely on uniqueness to solve which I find quite disappointing. Anyway, this puzzle wasn’t one of those and was quite enjoyable.
I used to enjoy bifurcating pencil puzzles because it gave me a chance to use my colored pencils. Now there are adult coloring books. I was way ahead of the times! 😂😂😂😂
Thanks for the explanations and for doing this exception video. ❤❤