The Computer Programmer's Favourite Puzzle

[@Rangsk]

A very cool puzzle by Clover! One piece of logic for "indexing" puzzles like 159 that you touched on but didn't formalize is that on the red columns vertically within a box you're always going to get one of 1-3, one of 4-6, and one of 7-9. This is due to the indexed digit not being allowed to repeat in a box.

[@HunterJE]

It is fascinating seeing Simon deduce what seem like big discoveries using indexing logic only to realize he's actually just doing standard sudoku logic through one remove

[@srwapo]

Huh, I've had a "feel" for that, but it's nice to see it formally stated.

[@PjotrV]

I was having the exact same thoughts during this video about the vertical theory :)

[@alexanderwales7870]

This was how I did the puzzle, and I think is a somewhat harder way to go about it, but it was the piece of logic that allowed me to place my first digit (before I'd seen that the center row is forced).

[@ChrisMildebrandt]

I didn't understand this comment until after I did the puzzle....I'm sure it'll help me on my next one of this type!

[@lucasdbarbosa]

I love the idea of how Simon completely forgets about Normal Sudoku rules when he is playing with a new rule that he`s not used to yet. He could put a lot of numbers just using Sudoku but his brilliant mind its just trying to see the new rule.

[@noredine]

"I reckon I'll have to do some sudoku. Bobbins!"

[@jeremydelillo900]

I just watched a video where Mark did the same thing in the past day or two...always kills me to see them miss the stuff they could put in sooner than they do

[@noredine]

@@jeremydelillo900 I just find it funny that he finds out what he could've found out easily using sudoku rules in a roundabout way using the other rules. i guess that's what happens when you're focused on the other rules, or maybe he just does sudoku as a last resort when he's still in the early stages of the puzzle

[@jeremydelillo900]

@noredine I was "that guy" yelling @ the screen about the 7's

[@patrickrodr]

@@jeremydelillo900 I was to. I was getting frustrated about the 7's it was right there just glaring at you. LOL

[@gordonglenn2089]

I love how Simon sneaks in a good vocabulary builder every now and then. Today's word was DILATORY, to describe Maverick's tardiness.

[@notnotandrew]

There's a word he used a while back in a video and now I can't remember it... it was a word meaning "a useless thing" and he used it in reference to a clue that had become irrelevant. If anyone can remember what that word might have been, it's bothering me...

[@notnotandrew]

Update: it was an adjective meaning "idle, lazy, or indolent" and the word was "otiose"

[@victorfinberg8595]

OMG. Amazing how my assessment of this puzzle changed from "Impossible, I give up" to "maybe" to "Yes! I am inwincible!" as the solution progressed. (The 9 in the middle, and all of row 5, was a gimme, however.) Amazing how one little bit of logic flowed naturally into the next little bit of logic throughout almost the entire puzzle (until the final, sudoku-only part). The trick is to crunch down the skyscraper clues, using the 159 part just as a sideline, and using the Goodliffe style.

[@itskittyme]

Whenever I finish a puzzle succesfully, I say: "What a beautiful puzzle", in Simon's voice.

[@chuckdecker3765]

It appears that at 07:40, Simon goes to "tidy up some pencil marks" and removes a 1 from R6C9, when he meant to remove a 5. Then the whole rest of the solve is built on the logic that a 1 can't be in that cell.

[@Dalixam]

Yep, he was lucky it seems.

[@bradle99CA]

It works out that r6c9 cant be a 1 because if it were, r6c1 would be a 9 and the skyscraper clue at the bottom of c1 would be broken.

[@ragnkja]

It’s fairly easy to eliminate 9 from r6c1 using the skyscraper clue from the column, but he does seem to have missed that step.

[@HunterJE]

@@bradle99CA Yes, but Simon didn't use that logic to remove the pencil mark, which is the very definition of "lucky" solving (marking, filling, or removing based on an error but the thing you marked, filled, or removed happened to be right anyways)

[@Tahgtahv]

@@kawaiisunzet Ya, I'm sure he would've noticed fairly quickly that things would break if he tried to put a 9 in r6c1. I don't think it affected the logic of the solve much at all.

[@Quaryu]

It took me more than an hour, but that's one of the first puzzles from this channel I solved! I'm so happy!

[@maverickstclare3756]

Maverick say: planes and skyscrapers should never be mixed

[@francescopetracca374]

44:56 Finally a skyscraper! And a 159 too! And not awfully hard to solve! THANK YOU CLOVER! 10/10 I ❤ it 👏👏💐💐

[@renecarling5653]

You’ve taught me so much about solving sudokus that now I’m the type to yell at my screen 🤣 thanks for reaching me so much!

[@curtissumner8578]

58:34. Clover is quickly becoming one of my favorite setters. Very tricky, but not overwhelmingly difficult

[@SmartHobbies]

What a clean looking design and easy to grasp rule set. Very nice puzzle, Clover, and great job on the solve, Simon.

[@epeo22]

I love that in one of the very few videos that Clover has in her own channel, she reviewed a puzzle by someone else with skyscrapers, and she said she doesn't like skyscrapers. Shows how we evolve by solving more puzzles, even at the high level!

[@doncook4097]

Here’s an example where the app should be enlarged and large as possible for the mobile users. I continually expand to see the pencil marks. Great puzzle. It didn’t give up until the end

[@christopherwessel5631]

I'm a computer programmer and new to sudoku but I've been watching this channel for a couple months and this is the first puzzle I've ever been able to solve before watching Simon. Thanks for being a great teacher!

[@TomHickey]

Loved the part where Maverick was being told off while Simon was on his victory lap, lol

[@inspiringsand123]

Rules: 02:36 Let's get cracking: 05:43 And how about this video's Simarkisms?! By sudoku: 10 (08:04, 09:44, 10:38, 10:44, 11:48, 22:46, 23:22, 26:01, 29:04, 30:18) Beautiful: 6 (04:27, 05:08, 10:02, 16:50, 19:05, 29:50) Sorry: 5 (06:32, 12:49, 23:14, 26:02, 28:42) Extraordinary: 4 (01:20, 01:29, 02:29, 05:49) Clever: 3 (10:00, 33:03, 33:08) Useless: 2 (26:02, 26:07) Maverick: 2 (32:28, 32:30) Stuck: 2 (27:51, 33:37) Brilliant: 2 (22:40, 22:42) Goodness: 1 (30:35) Bother: 1 (19:34) Naked Single: 1 (30:06) Goodliffing: 1 (06:22) Nonsense: 1 (15:13) Elegant: 1 (10:05) Off and Running: 1 (21:37) Approachable: 1 (05:25) It's Looking Grim over Bill's mother's: 1 (29:32) FAQ: Q1: What is a Simarkism? A1: A Simarkism is something that Simon and Mark typically or frequently say. Q2: How do you do this so fast? A2: I'm not made of flesh and blood, but of sand ... Q3: Why don't you include 'XX' and 'YY'? A3: Probably it's already on the list, but not mentioned in this video. But if you think it's not, tell me what you'd like me to include and there's a good chance I'll add it! Q4: You missed 'XX' at 'YY:ZZ'! A4: That could very well be the case! Human speech is hard to understand for computers like me, especially British sometimes! Point out the ones that I missed and maybe I'll learn!

[@nicosc2204]

how

[@derekfordyce9]

@@nicosc2204 Bot.

[@nicosc2204]

@@derekfordyce9 i know, but does it have access to the video before release? how can it scan the whole thing so fast??

[@inspiringsand123]

@@nicosc2204 I don't have access to the video before release. Computers are fast nowadays!

[@nicosc2204]

@@inspiringsand123 sure, how can you do it in few seconds though? the recognition of certain parts of speech require some kind of audio scanning (I'd assume), so how is it possible to do a half an hour of data and filter it in seconds? sorry if it's a too complicated question, or maybe I'm actually talking to a person now, idk

[@eytanz]

This was a really fun puzzle to solve, as Clover's puzzles usually are.

[@ctshirk7]

The absolute glee in Simon’s eye when maverick was too late.

[@Zendath666]

I must have missed out on the 159 style of puzzle before and I must day I love the concept behind columns indexing numbers like that.

[@glenjamindle]

I love how Maverick has become a reoccurring character 🤣 🤣

[@ericpraline1302]

The way this unfolded was a delight from start to finish.

[@whisperedshadow868]

This was the first one I've actually been able to solve correctly on my own. Granted I haven't tried too many, but it still felt great to do.

[@glennmelven3414]

MAveRicK;s timing was off today. Simon was exuberant about that.

[@michaelhird432]

Did we just crack this mystery wide open!? Mark is maverick!? It's been right on front of us the whole time...

[@noredine]

This is cannon

[@alainculos9294]

A very clever puzzle indeed, hard but not horrendously so. Convoluted but clean logical path. Beautiful. Thank you. Though I have to admit to needing a lot more than 33 minutes!

[@troy1565]

59:37 - I know it's not an impressive time but this is my first full solve before watching the video! Beyond thrilled!! Thank you clover and CtC!

[@flocktwo]

Wild to see the CtC/Tom Scott/motorsport connection with Mark on Tom's Second Channel, Tom uploading a video on the Nordschleife, and then Chain Bear doing animations for CtC (All within 48 hours!)

[@ragnkja]

The TSp video with Mark went public a bit more than 48 hours before this one, but yes, it’s all pretty close together.

[@stevieinselby]

I don't know who Chain Bear is, but they did this animation quite some time ago, and it regularly gets wheeled out whenever Simon or Mark is solving a skyscraper 🏢 puzzle.

[@jackw7714]

@@stevieinselby If its the guy I think it is, then he does Formula 1 and other motorsport videos of a very high quality. His animations do look like this so I guess it is him!

[@jackw7714]

Just checked this out and Liv Boree and Medlife Crisis is on it, bloody hell, I love them all.

[@HunterJE]

Ahh yes, two variants that always seem straightforward but my brain breaks trying to apply them

[@Rubrickety]

What a delightful ruleset. This was actually the first Skyscrapers puzzle I've tackled, and I think the combination with 1-5-9 rules was rather helpful.

[@SeriousPigi]

Lovely puzzle! Thanks to Clover and CtC!

[@doriswlongAgoandfarAway]

Thanks Clover. Well done Simon.

[@matthewender3473]

A very nice setting by Clover, as always!

[@tehjoch]

79:46 is the final count, great puzzle! I've lost a long time getting the 7 in row 7 but after that I was able to keep moving again

[@Coyotek4]

14:07 ... for whatever reason, I tend to do well with puzzles by Clover the Clever. (I can't help myself; comes from a decade of watching MLP with my daughter.) Loved solving this!

[@susanne5803]

53:47 without help. My brain feels like after several rounds of stroop tests ... I really like this combination of restraints but it does cause brain sprain! Thank you very much!

[@jcmarriott9723]

At 25:10, Simon is trying to find the 6 and 8 in row 8. Why not look at the 7? It only has one valid space, r8c4.

[@user-yl3pp8fy9w]

Gotta extend view time for ad revenue

[@bertbergers9171]

@@user-yl3pp8fy9w that would be very cinycal. But you might be right :( Sad how KZbin corrupts some channels and with that pollutes trust in joy and sincerity.

[@superdan2593]

I also spotted this 4 minutes before Simon. I'm quite proud of myself actually. I don't really do sudoku, I've just been watching this channel for 2 weeks now and I'm learning a lot.

[@Mrkaiable]

I was screaming at the screen at that very moment! Thanks for the acknowledgement.

[@DubioserKerl]

I am a computer programmer and I approve this rule set very much. While Phistomephel makes monstrous but beautiful puzzles, Clover makes... just beautiful puzzles.

[@GuilhermeCarvalhoComposer]

Took me a bit over an hour, but I managed to solve it. Really a very nice puzzle, and probably the first skyscraper one in which I felt comfortable. Well done, Clover!

[@Tombsar]

I like doing standalone Skyscraper puzzles (Towers in Simon Tatham's Puzzle app), so I really enjoyed this one. 28 minutes, which I'm fairly happy with.

[@redpepper74]

This one was so satisfying to solve, the indexing and skyscrapers went really well together!

[@lewsouth1539]

A handy rule for these 1-5-9 puzzles: In each box, the “index” cells must contain one low digit (1-3), one “medium” digit (4-6), and one high digit (7-9). [23:13] “Sorry, I'm just-I'm getting distracted by my brain. Brain, stop distracting me.” Yes, brains can often be rather troublesome that way. A lobotomy might help.

[@G4M1L]

I found it funny how Simon immediately got to "goodliffing" the perimeter cells next to skyscaper clues. Not an unnatural strategy, but not really necessary. Whereas I - usually much more like Mark in that respect - didn't start that until way later and instead focussed on the pencil markings arising from the combination of indexing and standard sudoku rules. :-)

[@evlredsun]

I do love Simon's joy at solving and understanding puzzles, there have been countless knowledge bombs and not quite as obvious insights I have learned from him that seem so obvious once pointed out. Little things like knowing there are always 1s on 6/7/8 arrows. I don't know if I ever would have realised that, even though it feels so obvious now, and an integral part of arrow sudoku. As an aside, i now feel confident in tackling SET based puzzles thanks to Simon's videos, not only in sudoku, but set theory and linear algebra / matrices in general that I never really understood until CTC. While this trick is not quite as ground breaking, I feel like he is missing a similar aspect of 159's and I only hope that he reads this before future 159 videos. In any index , the indices in the same box must be from a low (123) mid (456) and high (789) to show that their respective entry/ies is/are in three different boxes. For this puzzle in particular, this was really helpful at disambiguating some of the high/high or low/low pairs showing up that otherwise took a slightly harder path to resolve, especially with the more limited column clues. In several other 159's I have solved this plays well into roping or roping-like logic paths as well, or at least pencil marking and ruling out low/mid/high. I don't know if it is ever required to solve an index puzzle but it can shortcut some of the steps at various stages, especially marking up early indices ... just a small trick to add to your collection. SPOILERs EG1, in this puzzle, you have the sets of 2/6/9 - 1/4/8 - 3/5/7 (low/mid/high) indexing the 1's, showing not only the respective column allocations for the 1's, but also the left/mid/right for the boxes wrt the sets. EG2, In column 5 (index5) nearing the end of the video/solve, this could have helped limit several possibilities that took 1-2 extra steps of logic to resolve. Likewise in column 1 (index1) nearer the start: knowing that r8c1 and r9c1 were both low/mid means r7c1 could only be high, giving the 78 pair much sooner as well as in turn ruling out the mid numbers from r9c1 (and therefore low in r8c1) due to the skyscraper, etc. Hopefully that makes sense. I really do enjoy the 159/index puzzles. I think there is a lot of potential to play around in them. I hope to see some more crazy variant combos coming up soon! I can't begin to understand what goes into a puzzle like this but my brain gets whirring on column/row combo indexes that might only need 2-3 variant clues to solve... the skyscrapers were a great way to showcase the logic involved in an index puzzle. Anywho, Thanks for another great puzzle, Clover, and another enjoyable solve, Simon!! EDIT: apparently quite a few other comments (that i did not read before posting... clearly) pointed out this trick but hopefully my examples show how this would have been useful in this particular puzzle.

[@Jdog7117]

Love these skyscraper puzzles, would love to see more of them.

[@Bonar09]

36:38 for me. I really liked the skyscraper logic - great puzzle!

[@MitchellD249]

As a professional programmer who had never done either a 159 or skyscraper sudoku before, I can confirm that this was a joy to solve! The skyscraper rule especially seemed daunting at first, but I managed to get my head around it pretty quickly and loved how the rules interacted with each other. Beautiful puzzle for sure.

[@eclectichoosier5474]

Great puzzle, Clover! (As always.)

[@sudokuclover9111]

I believe the swordfish 159 you mentioned was by Shye :)

[@jdyerjdyer]

Thanks for the 50 puzzle pack. Looks like I'm going to be busy for quite some time! lol :) Also, can't wait for my copy of CtC Greatest Hits!!! Coming so soon!!! Excited doesn't even begin to describe the feeling!

[@ShinyTogeticFTW]

I am extremely proud of my 1 hr 6 min 11 second solve time on this puzzle! I will admit I spent quite a while processing everything, both before and after figuring out the row 5 two-sided 5-high skyscraper view clue, but I managed to complete it without peeking at the video for hints; I always pause at "Let's get cracking" and then see how far I can get on my own.

[@Stephen-Fox]

Very smooth solve path, very enjoyable. 24:56 solve for me. Cheers for showcasing this.

[@ojojojojojoje]

Thank you for the name of the video, the choice and overall amazing work :) As for a starting programmer, solving this before watching was a great boost for my confidence :D Have a lovely day ya'all

[@auroran0]

I was watching this when I heard an airplane and was waiting for the comments about Maverick, so I paused the video and was still hearing the aircraft. I guess he had to buzz me before getting to you. 😜

[@leaksfoos]

What a lovely ruleset, took me 60 minutes but really enjoyed it!

[@VeritasUnae]

Loved this puzzle a lot, the deductions just kept flowing and I adored the information you get from row 8 a lot! Took me 42:02 minutes but I'm so glad I gave it a shot. c:

[@rasmusvanwerkhoven1962]

22:18 “so this is 3, 4, or 5, and that is indexing the 1 in this row. It’s not 4,“ Me: “Because there’s already a 4 in the 1st row,” “Because the 1 would clash” Me: “... that works too, yeah”

[@twiggywales]

I would call this approachable. Especially compared to some of the recent ones

[@mahmoudabdelghany7112]

Very elegant idea.. very clever and fun.. ty CTC and ty Clover ❤️

[@zdibs]

Clover is really becoming my favourite setter. Mentioned it on Mark's GAS video the other day, but they really set just difficult enough puzzles for me currently. ^_^ Granted, I did get stuck at the point you reached @24 minutes in for this one. For about 20 minutes until I realized a 7 had to be in R8C4 and R9C8. (Because a 7 in R8C8 would make a 4-high skyscraper and every other 7 is blocked by other 7s.) Oh well, still happy with solving it. :)

[@ozlich]

I really enjoyed this puzzle! Thanks Clover 🍀

[@solentsinger]

"A festival of pencil marking"!!😆

[@scotfritz34]

Screaming at Simon to put the 7 in row 8!!! Lol we was stuck for a few minutes and I was waiting for him to see it.

[@srwapo]

22:58, I'm starting to feel comfortable with this constraint, though the negative implications still trip me up sometimes.

[@gregind01]

"Too late Maverick!" 🤣🤣🤣

[@teliots]

Not sure what the puzzle has to do with programmers, but it would probably be liked by professional rock climbers. A '1-5-9' is a famous challenge for elite climbers, and some of them even climb skyscrapers!

[@maverickstclare3756]

One indexes an array, there is an eternal argument whether indexes start at 1 (Fortran & Julia) or 0 (C family). 1, obviously, is the natural choice. 0 is a leaky abstraction.

[@teliots]

@@maverickstclare3756 True, programmers do love to waste time arguing over 0 or 1-indexing. ;)

[@masamaeda9217]

@@maverickstclare3756 I wouldn't call 0 a leaky abstraction. Id argue it's not an abstraction at all, it's syntactic sugar. Array indexs roughly translate to an offset off of a base address so pointer[index] is the same as pointer + index. Using 1 would require far more processing or be very inefficient. C was created to be fast, compile fast and not require a lot of memory. Although these days that doesn't matter nearly as much. That being said it's definitely a relic of the past(sorta). Id argue though that it makes reading raw memory a whole lot easier.

[@dirk5697]

@@masamaeda9217 someone gets it :). Also still makes sense today for the same reasons (and for things like indexing the last element, that often can be done by syntactic sugar like e.g. in python using [-1])

[@gregorymorse8423]

0 is the correct indexing abstraction as it fits the storage model so if an array points to the memory address with the first unit of data, then adding 0 to such a pointer and dereferencing gives the value. Of course indexing can be done by 1 or any other value and for mathematicians when using natural numbers, 1 might be more convenient, but for programmers, the correlation to a storage mechanism is logical. Every language can do what they choose of course, but generally since the days of C using this abstraction, it has become widespread and the norm.

[@BradTorresHTX]

Wonderful puzzle. Wonderful solve. The brief bout of heptaphobia had me laughing. Truly clever puzzle.

[@tmmlis002]

My favourite rule set. Had SO much fun! Thank you 😊.

[@isidrogonzalez7481]

"Things are going remarkably well... probably famous last words" 😂

[@_-_-Sipita-_-_]

Well, 159 sudokus have a huge weakness that idk why ppl aren't talking about: Each 159 column is very restricted because each triple of digits in the same box must have a "123", a "456", and a "789", because the number in the x axis mustn't appear in the same box. That means the 5 clues of C1 and C9 are inmediatly restricted for the 789 that must appear on one of the first 3 digits seen by that clue.

[@tehjoch]

considering I just read your comment 5 times and can't understand what you're talking about may be a reason why some ppl like me aren't talking about it

[@Alex.S.1]

Very beautiful combination of two of my favorite rules.

[@sampathkumar-ej7xl]

This indexing rule can be confusing but the puzzle was satisfying to solve. An easy enough opening with the two external 5s on the same line but other digits had to be slowly extracted.

[@markp7262]

17:05 finish. Love skyscrapers and love 1-5-9 puzzles. The mix of the two was very fun!

[@bristolrovers27]

Nice puzzle I'm very glad Simon eventually concentrated on row 8

[@sanabas1]

@16:00, it is useful, because one of the tricks with 159 is that in each box, column 1, 5, 9 must have 1 digit from 1-3, 1 from 4-6, 1 from 7-9, because if they had more, it'd put 2 x 1/5/9 in whichever box they're indexing. So r1c9 must be 13, r2c9 must be 456, and r3c9 must be 7, because it can't be 8 or 9. Same for r7c1, it must be 7. Can get those 2 7s before you have any other digit, because box 7 c1 and box 3 c9 must have 1 of 7/8/9 in them, if it's 8 or 9 it breaks the skyscraper clue, and if the 7 is anywhere but r7 and r3, it also breaks the skyscraper clue.

[@idannen]

Yay! It took me 45 minutes, where usually my times are closer to 2x the time of the video. I enjoyed this.

[@alexanderwales7870]

Some interesting logic on this one. The lower left and upper right skyscrapers actually allow you to immediately "force" two sevens, since each set of three in a box must contain low (1-3), mid (4-6), and high (7-9) digits in order to avoid collisions with the indexed number. The high digit in the first box the skyscraper looks at must be a 7, because otherwise you ruin the skyscraper.

[@CauchyIntegralFormula]

13'22" is what my clock reads, but I got interrupted and paused but forgot to restart for a bit, so probably more like 18-20 minutes. I was very impressed at how forcing those 5 skyscraper clues were

[@alexm.2960]

"programmer's favourite puzzle" has css in the thumbnail.

[@Wecoc1]

Lmao

[@Raven-Creations]

At 24:55 row 8 is the key. The digits 678 have to appear in order. To allow a 6 before it, and an 8 after it, the 7 can only go in C4, and by sudoku in R9C8. Back in R8, the 6 must be before the 7 and therefore in C2. The 8 must be in box 9. I'm surprised that Simon struggles with this ruleset. I know one can have a mental block, but it's usually along lines like visual vs mathematical. This seems a very specific block. I did have a similar problem myself with the recent GAS and the 6x6 sandwich puzzle. I've done so many normal sandwich puzzles that my neurons are tuned to working with 1s and 9s, and a 45 total for the row/column. The 6x6 should have been much, much easier than a 9x9, but my neurons were continually forcing me down the wrong path and I struggled, sometimes even putting 9s in the grid. I do like Clover's style. Her puzzles are always very clean and elegant, always have a nice flow, and they usually resist all the way through, rather than collapsing after the break-in.

[@Xiuhtec]

I'm pretty proud of my fastest solve so far at 58 minutes. Got the entire center row in 2 minutes flat when immediately seeing the force. First time solving a puzzle with the skyscraper rule, it's very powerful.

[@Gonzalo_Garcia_]

19:02 for me. I like the 159 variant, not too hard but it works really well for more approachable puzzles. I missed a skyscraper clue for like 5 minutes at the end and thought the puzzle had more than one possible solution, but luckily I was finally able to solve it.

[@DWestheim]

Wow. I managed to solve it under the video time (29:21). Fortunately the entry was obvious, given the absolute scarcity of clues. And I never did well with skyscraper sudoku, but perhaps the simplicity of the all-5s helped me there. I want to thank the guys on this channel for working tirelessly to sharpen my numb brainz over the last 2-3 years. The puzzles seem to get wickeder all the time, but I'm now able to solve them over half the time (not even counting GAS :-P)

[@l3igl2eaper]

52:26 I loved that puzzle! My first time ACTUALLY getting through a skyscraper without watching the video for hints!

[@jkid1134]

Such a cool puzzle! And I forgive you for (aggressively) missing the 7 in row 8 question.

[@iabervon]

It's funny how much more used to skyscrapers I am compared to Simon and less to sudoku. I kept being blind-sided by the box rules applying while Simon kept missing limitations on where digits of various sizes could be. The 7 thing he didn't notice for a long time is the main sort of thing you work from in a skyscrapers puzzle, so that was where my attention went immediately. I was also befuddled by the fact that I do skyscrapers with negative pencil marks, but sudoku with positive ones, so I ran out of ways to mark cells on the computer.

[@CMLachky]

Great Puzzle!! Awesome logic, and good difficulty!

[@integralmystery]

Nice to complete one of these around the length of Simon's total video length - surprised to then watch him pencil mark in 12345 at the start of the skyscrapers when I jumped straight to finding potential positions of the 9's which felt much more useful

[@jRoy7]

25:18 It's funny how you color the 6s instead of penciling them in, and the 8s you said it'd be natural to go there so it probably isn't a good thought. Although by the logic you just explained (6-8 have to be in increasing order from left to right) you actually know the 8 can only be in those 2 spaces and could pencil that in too. :)

[@dennisc3438]

It can be in 3 places: column 4, 7 and 8.

[@TheGreatPurpleFerret]

@@dennisc3438 that doesn't matter anyway since the 7 in row 8 can only go in column 4.

[@maaleru]

@@TheGreatPurpleFerret 6 here or here, 8 here or here... Then he goes into other area... But 7

[@Kinada]

Something to remember when doing this variant is that each set of 3 red cells in a box can have one of each set of the digits 123-456-789 so when you find that a cell can only be from one set any digit from that set can be removed from the other boxes.

[@robynrox]

I enjoyed that one! 48m 59s for me. I recognised fairly early on that for each of the shaded cells in each box, there would have to be one digit from each set of [123] [456] [789] because otherwise the indexed digit would appear more than once in a box, which would of course be impossible. Nice!

[@svennielsen633]

The most known person in sudoku who has not appeared on screen: Simons neighbor.

[@penningmeestercgkdelft9159]

27:57 because the 7 cannot go into r8c8 (because of the r8 skyscraper clue), the 7 is locked into r9c8 and into r8c4 !

[@michaelhoffman2011]

Woo back on track.. Took me 32 minutes. Very clever puzzle.. I think I am starting to get used to the 159 pattern, but it still makes my brain work pretty hard lol

[@dwarfigplays9806]

Nice one! 40:32 for me. Those rule intersections were preety fun to find!

[@leojs5673]

For whatever reason 159 rulesets always confuse me a lot, but gonna give this a shot 😄

[@srwapo]

It takes a minute to wrap your head around it. There's a few ways that they interact and one needs to be aware of them all.

[@mikepictor]

Nice. Not too hard at all. Not a pushover either, but it keeps revealing if you're patient.

[@stevieinselby]

Lovely puzzle 🍀 ... took me about 40 minutes, not helped because I kept trying to index the white columns as well as the red ones (hey, it's late and past my bedtime!). I really like this kind of ruleset where you need to think logically about it, but there are no ridiculously complicated deductions and no geometry or SET to worry about (because I'm terrible at spotting them).

[@osirusbrisbane2305]

Fun Puzzle! Took me a bit to grok the logic, but then it was a very enjoyable solve path.

[@pimanrules]

It can't be a programmer's favorite puzzle if it counts from 1 lol

[@MeriaDuck]

Given that this app can display zero, a zero to eight sudoku should be possible. That would be quite a mind bender, the secret not being what it used to be etc...

[@BrooksMoses]

34:15 for me -- almost faster than the video time. Not bad, given that I typically need about twice the video time. I suppose this correlates with me being a computer programmer. :) I really liked the opening, and how there were several steps with just barely enough information to make the next step.