Important Skills to Solve Classic Sudoku

[@jurjenvanderhoek316]

I love to see you do a classic Sudoku again. Please do more!

[@SmartHobbies]

Please feature more Classic Sudokus! I love these videos and puzzles like this from Kyle.

[@emilywilliams3237]

I know that classics are near and dear to your heart, Mark, and it is such a pleasure watching you work your way through this one. It was a great chance for you to both demonstrate and describe the Synder system of marking, as well as show the effect of some particular combinations of digits (y-wing? or whatever they are called!), and especially the value of coloring as a technique for solving. Thanks so much for this video!

[@Apocryphate]

Can anyone explain to me how the “skyscraper” (along with other “if this is then solving becomes impossible”) shown in this video wouldn’t be considered bifurcation? My understanding of bifurcation is that you’ve narrowed something down to two possible values, you then prove one of them incorrect by using the value and following the logical implications to a failed state, thus proving the other option correct by deduction. This is precisely what is done several times in this puzzle, yet Mark states, “You couldn’t call anything there a bifurcation.” Whether you label it a “test of logical soundness” or a “guess and see what happens,” the process is the same. You’re proving that one value is correct by proving that the only other remaining option is incorrect, and that is accomplished via playing out a scenario to the point of failure. I don’t even understand why bifurcation seems to be frowned upon, as it’s a valid tool of logical analysis, but that’s a different discussion entirely.

[@inspiringsand123]

Rules: 02:10 Let's Get Cracking: 02:27 Mark's time: 25m02s Puzzle Solved: 27:29 And how about this video's Simarkisms?! Ah: 7x (05:00, 07:43, 08:58, 10:52, 17:13, 17:13, 23:19) Obviously: 5x (02:10, 13:59, 22:12, 25:22, 25:41) Sorry: 3x (06:40, 18:35, 22:49) Wow: 3x (00:47, 08:24, 20:27) Pencil Mark/mark: 3x (12:30, 26:21, 26:43) Clever: 2x (18:40, 27:29) Lovely: 2x (11:30, 21:54) Surely: 2x (24:30, 24:55) In Fact: 2x (05:39, 17:44) What a Puzzle: 1x (04:14) Missing Something: 1x (06:07) Bingo: 1x (23:19) Stuck: 1x (04:54) Brilliant: 1x (23:39) Intriguing: 1x (00:55) Progress: 1x (06:27) Most popular digit and colour this video: Nine (70 mentions) Purple (26 mentions) Antithesis Battles: Row (13) - Column (12) 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!

[@chris5619]

Haha, Mark said "do do"!

[@swanlipsgomez1]

Huh,huh…huh,huh, he said do-do. Heh heh heh. God bless butthead.

[@bertbergers9171]

This was a nice hard nut to crack. Found stuff and then pencilmarked the whole thing and had to make some big chains to get on, but finally got stuck. Had to take a peek as i was not going to backtrack all the way to the start :$ Never tought about colouring to help my self, which would have helped as you proved. Thanks for the video @Mark and for the puzzle @Kyle Vandeveer

[@Qazqi]

At around 11:55, the way I saw it was a finned X-wing on 9s in r47c34 plus the fin being r7c12. The X-wing rules out 9 from the 89 cell and the fin being 9 also rules out 9 from the 89 cell. Around 21:30 is where the skyscaper comes in with 3s in r2 and r6. The skyscraper eliminates 3 from cells seen by both r2c6 and r6c4, namely eliminating 3 from r5c6.

[@paulakeay4317]

I finished the puzzle in only double Mark’s time, so I’m rather pleased with that!

[@RichSmith77]

At 10:54 (about 3s) "I thought I was onto something there. I'm not." Oh, but you were so close! 🙂 As you say, a 3 in r5c7 forces a 3 into r2c9. But you missed that a 3 in r5c6 (the only other place in r5) would also force a 3 into r2c9 (via row 2). So r2c9 was always a 3. You got it ten minutes later (@21:28).

[@Mephistahpheles]

@11:05 So pleased with myself for spotting this: "If that's a 3..." OR that's a 3.....forces the 3 in box 3. 🙂

[@ElDillas]

Good morning from New Zealand!! - Cassadilla

[@peternamey4430]

Great puzzle and I enjoyed Marks solve. Nice to see a classic sudoko for a change too.

[@neokart2660]

11:50 I'm not sure it's a Skyscraper, but it does "work" like one. What is 100% a Skyscraper was the scheme that you found previously with the 3s at minute 10:20 You could cleanly rule out the 3 on r1c7 and therefore place it on r2c9. That would have avoided some problems later in the solve. Great video as always. Greetings

[@cathybryant5119]

I also did this. I only saw it because Mark mentioned the positions of 3s in rows 2 and 5. I took the analysis slightly further than Mark did, which resulted in the 3 in box 3.

[@AaronPriceColby]

Woof, 01:32:42, also needed help to find the first turbot fish but good practice, helped me figure out other impossible cycles later on.

[@shawnmichajluk2044]

Great puzzle! What Mark did with 169, I also followed with 46 and 58 to see if a cell conflicted being a 4 or a 6. Great trick! I would have never seen it otherwise.

[@dodekaedius]

Awesome solve

[@Raven-Creations]

Very nice classic. We don't see enough classics on the channel. I had got all of the 3s quite early on, which made some of it a tad easier. I can't recall exactly how I got this, but I had a 37 pair in C7, and it would only work one way round. This also gave me most of the 8s. I had some 146s, so I coloured them and the 46s allowed me to identify which was the 1. The remaining 46s were used to make other eliminations, until I finally placed one of the 46s on a 6, allowing me to finish off. I had started to comment that your initial red/yellow colouring was mad, but you spotted your mistake, and also thankfully spotted that they didn't have to include a 9 (even though they did in the end).

[@QwDragon]

21:58 To get rid of color you should've switch to colors (V) and then doubleclick the cell.

[@srwapo]

30:35* with an asterisk because I had to look at the video for the logic numerous times. Not sure I would have seen it on my own, but hopefully I learned something.

[@mudscuffer]

Broke it with my 5th digit, restarted after a while and solved in 34:25

[@JohnRandomness105]

8:10 I decided to follow Mark's logic with 9 in R8C3. He shows that R7C4 must be 9. With my grid further filled, I also got that R4C4 must be 9. Therefore, R8C3 had to be 8. That cracked the puzzle for me. 10:00 I can see it now. If R8C3 is 9, then both R7C4 and R4C4 have to be 9. 10:10 "I haven't seen any X-wings or Y-wings here yet." I found a skyscraper in 3s that placed a 3 or more, and an extra-strength finned X-wing in 6s. 19:20 I can see the skyscraper in 3s, in columns 4 and 9. It places the 3 in R2C9. 22:10 The skyscraper was found and applied. Now, a finned X-wing or empty rectangle in 6s is in rows 2 and 5 -- take your pick. (I call the position an extra-strength finned X-wing.) 23:40 You did the equivalent with red and yellow.

[@reganmartin5412]

Struggled, but still fun! Thanks!

[@ChlorieHCl]

12:00 It's a turbot fish (length-3 X-chain), and skyscrapers are special cases of turbot fish. The logic of a turbot fish goes: If A isn't X, then B is X, then C isn't X, then D is X, so X must be placed in at least one of A or D, thus all the X's that see both A and D should be eliminated. In this case, X=9, A=r4c3, B=r4c4, C=r7c4, and D=r8c56, so as a result, since the 9 in r8c3 sees both r4c3 and r8c56, it should be eliminated.

[@Not3xactly]

The logic to elimate 9 from column C row 8 is an empty rectangle on value 9 in box 8.

[@bait6652]

That 9 trick was nice.. Didnt think one could apply Pf-ring but i did get the 18pair in B4

[@davidh.4944]

38:46@#4236. As is so often the case with this kind of classic, I ended up with a fully-marked grid, which I resolved with a series of empty rectangles and a final coloring of 46 pairs. Not bad.

[@grahamrskelly6042]

Enjoyable video, of a good classic!

[@wanderlustwarrior]

19:59 for me. I don't really know how I was supposed to spot the path outside of intuition, but I did it.

[@Enkil01]

Enjoyed this, made a nice change 👍

[@danielwolters9082]

Nice puzzle, thank you 😊

[@11SHADOWSNAKE]

Hi Hero’s, 16th of september is my brothers 24th birthday! He is a big fan and he is the reason I started watching your (amazing) videos. Could you wish him happy birthday this saturday? He would love it. Thanks anyway for the amazing content! ❤❤

[@CrackingTheCryptic]

Presumably we don't need to know his name to wish him a happy birthday?

[@Alliappalachian]

Thank you for this!

[@piarittersporn]

Beautiful classic

[@beamer908]

Not sure this gets you all the way there but at 20:10, aren't 46 in r5c1 and r2c3 (the red highlights) a "pair" in that they have to be the same-both 6 or both 9? And given that, doesn't that rule 69 out of r2c1 and r3c1 and make those a 18 pair and place a 9 in r7c1? This got me further and wasn't sure if anyone else spotted it.

[@Rach881101]

26:52 for me. Nice puzzle!

[@bokmcdok]

This is the weirdest rules set I've seen for a puzzle on this channel

[@ValeriePallaoro]

Anybody? I just figured out that it's called a 'swordfish' because we use it to 'fish' for numbers .... Is that the case? 'cause it's been bugging me for a while.

[@klassenlm]

Timer says 11:00 for me with some backtracking included. Other than my own mistakes in didn't find anything unapproachable.

[@RoderickEtheria]

I'd argue this puzzle was hardly genuinely approachable. There was a hefty amount of spotting where certain digits ruled out others of the same digit from rows or limited others of the same digit to a single spot in a row that a beginning solver would not begin to figure out.

[@muralip2052]

At last a classic!

[@awilliams1701]

The classic, arrow, and killer apps have all been recently updated on android and have the new interface. arrow (that have killer or sandwich) and killer are now playable on my tablet!!! I don't believe sandwich or miracle (that contain killer or sandwich) are though. Anyway I love these updates, but I would really love it if I could get them on steam as well. I love the new interface better than the old one. Last time I checked classic (the first to get the update) still had the old interface and didn't have smart hint on steam.

[@ianagol]

What is the configuration of 3s at 21:14 called? I suppose it’s some sort of jellyfish, but it surprised me that it resolves the 3s.

[@davidh.4944]

It can best be seen as a skyscraper in C4 and C9, or an empty rectangle using B3+R5. That's how I spotted it. There are several other empty rectangles available within the same batch of cells. I believe you can also view it as a finned swordfish in C479+R156, with R2C9 being the fin, but that's bit hard to spot since the elimination unusually crosses box boundaries. I may be wrong about that, though. Edit: Yep, definitely wrong. There is a jellyfish in C4679, but it has no sting. Very often skyscrapers, empty rectangles, and fish are all one and the same, but I just don't see a working fish pattern in this one. Edit again: I got it. It's a finned x-wing. R15+C67, with R1C4 as the fin. Either the x-wing takes out R2C6 or the fin does.

[@philwhiting5625]

3:30 how did you know that was a 6 and not a 6 in one of the 2 on the right? You explained it but i dont get it

[@davidh.4944]

It's a simple naked single. R9C2 sees 145789 in the row, and 23 in the box and column. The only number it can be is 6.

[@luketurner314]

27:34 for me, only a couple minutes longer than Mark

[@_aullik]

I got stuck on this. After an hour i referred to your video and i missed the 8 Y wing.

[@awilliams1701]

no one: my brain: The 2 in R1C3 and the 2 in R5C9 means there is a 2 in R3C7....right next to the 2 in R3C8......oh......wait........ LMAO

[@shadow-wulf]

I need a start to finish teaching order in your videos. As much as I've been enjoying watching them this week, i don't find it easy to follow.

[@MohdShamlakh]

I solved it

[@bruceh8043]

30:22 for me and solver #1319.

[@Gonzalo_Garcia_]

11:31 for me. Nice puzzle!

[@adrianjcox8611]

Love your channel but: I am probably a bit dim but I didn't understand what you were doing with the colouring at all. just lost me completely and often you go a little fast and don't explain clearly enough for dullards like me to keep up. I just gave up.

[@Pritchie45]

50 minutes

[@DaleKingProfile]

Was it just me or was video and audio slightly out of sync

[@trudain]

13 mins for me, but I bifurcated....

[@Apocryphate]

So did he. Several times in fact.