Extreme Sudoku: Wings, Skyscrapers & Empty Rectangles

Simon takes a look at this "extreme" rated puzzle requested by one of our viewers. As usual, these solves allow us to showcase some exotic techniques. This time we have x-wings, y-wings, skyscrapers and empty rectangles!!
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#Sudoku
#crypticcracking
#commitsudoku
#xwing
#skyscraper

[@DougalAAllan]

Possibly one of the most instructional videos on the channel. X-wings, Y-wings, Skyscrapers and Empty Rectangles all shown and explained in clear terms with visual aids besides. Glorious.

[@shadowfox1221]

That's one reason I love the channel, I'm learning all these tricks.

[@jojoj81Gaming]

who's here in 2021 smiling at Simon apologising for a 27 minute solve.

[@ZedusUA]

2022 :)

[@hargrim6892]

08/02/2022 :))

[@shadowfox1221]

2022 as well

[@ChrisParr]

Just watching to try and get my head around empty rectangles and being so impressed by how far the presentation and the software has come. :-)

[@omar_vlogger]

2023 hello

[@notchinthebedpost6087]

9:00 skyscraper 12:40 x wing 16:45 empty rectangle

[@preciousghouls]

notchinthebedpost 24:25 y wing

[@olliehopnoodle4628]

@@preciousghouls 25:50 final sky scraper

[@olliehopnoodle4628]

I would also note that he changes notations at around 10:30. He recognized the skyscraper at 9:00 but not using the 'standard' notation. It took me a while to realize that often the skyscraper, xwind, empty rectangle can be hard to see with the standard notation.

[@YouTubist666]

12:31 naked triple in row 8, 1-7-9; you can resolve the 5 in two cells.

[@othafakk]

15:01 "I feel like I'm missing something here." Shouting at the screen "The five in the 8th row!!!"

[@olliehopnoodle4628]

I know. Sometimes I imagine if someone is looking over my shoulder and they see something obvious and I don't see it.

[@RebelScumbag]

Dont apologize for taking extra long time. Some of us are learning the logic instead of brute force

[@cadmar2969]

Beautiful! Do enjoy the logic and the step-by-step explanation using empty rectangles and skyscrapers!!!

[@pedroslots184]

Really appreciated the logic at the end rather than the 'brute force' so thank you for that. Not that I have anything against the speed solving techniques, just a fan of the logic more.

[@bonkers_dave]

It is insanely gratifying to spot something that you miss, because it does not happen often, and usually you are on it within a minute or so. But in this case I noticed at 12:29 you had 7-9,1-7-9,1-7-9 in row 8, which leaves a 5 only in column 6, which lets you place two 5's at that point. It took you until 21:30 to place those 5's. Maybe there is hope for me after all! I'm sure others have pointed this out, but I did not read all the comments. Just basking in the glory...

[@lestersullivan2055]

You explain that so beautifully. Thank you. Now if only I could just recognize these situations when they arise. Spotting them as I work though the puzzle seems to be the hardest part. I guess it just takes more practice.

[@sdrawkcab190]

The additional drawings really help demonstrate the difficult concepts. Thanks for continuing to add them!

[@danielleanderson6371]

21 minutes in and I realized the video is tagged with #commitsudoku. Holy smokes, Simon.

[@aseloss]

what does that even mean?

[@brian7168342]

@@aseloss if you google image search commit sudoku, it will show a drawing of a Japanese man committing seppuku, except it is a sudoku board cut into their chest.

[@ghosty918]

Confusing the word Sudoku with Seppuku became an internet meme

[@angelmendez-rivera351]

@@aseloss The Japanese word "seppuku" is the name of a particular procedure by which samurai historically would commit suicide if given the orders to do so or of their own will, which is done by stabbing a katana into the middle of their torso. Another name you may see for this is the word "harakiri." For reasons I have not bothered to research, people on social media started using the word "sudoku" instead of the word "seppuku" when talking about committing suicide by the process explained above. Thus, in meme culture nowadays, people associate the phrase "commit sudoku" with the act of committing suicide. This is why the OP was shocked at seeing "commit sudoku" as a tag for the video.

[@ThatGuy-dj3qr]

Thanks so much for taking the time to explain the many techniques that you use. I am really learning a lot from you and from these videos.

[@LuisHartmann]

These videos just made me addicted to sudoku... and this video made a really good job at explaining these techniques

[@ugyennorbu9443]

That was one roller-coster ride of logic.. Great work as always..

[@Lohoydo]

This video taught me more than most others combined. Taking the time to explain not just the logic of a wing, skyscraper etc. but how to find them helped immensely. A well chosen puzzle for the tactics too as the wings, skyscrapers and empty rectangles abound. I ended up solving it using several different combos than he did

[@perry4754]

Thank you for that great explanation of empty rectangles. (and the other techniques but especially empty rectangles)

[@renaunap2509]

New to sudoku world and I'm mad I didn't learn sooner... sudoku is great. Thanks for explaining in a way my beginner's mind could understand. 🙏🏽❤️

[@fiqihfandrian8416]

So fun watching you ending the puzzle! More of this please!

[@PaulaZF]

A great tutorial in the X-wing, Y-wing, skyscraper and Empty Rectangle in one swell food! Thank you!

[@MrBrexan]

Great explanations! This really helped things click for me. Thanks for showing so much in one video and trying to find those patterns rather than just solving

[@FGL_tv]

As someone who's only recently started playing, I greatly enjoy the videos. The in-depth explanation is very helpful!

[@thorexu6017]

Thanks Simon for your superb job to crack this sudoku puzzle.

[@sweetpeabrown261]

Huge help. Thanks. I couldn't understand how the the hints worked till you explained it so patiently!

[@cleddau]

Don't worry about the length of the video, the content is good and worth it.

[@KTSpeedruns]

I copied this into a web program that lets you build one and try what you build. I had two failed attempts that ate over half an hour each. Then, my successful attempt took 50 minutes. This puzzle was agonizing. In all my attempts, I didn't notice the 2 in the bottom right box anywhere near that early. It was more like I was half way through the puzzle before I filled in anything in that box. Now I'm feeling like a fool for not noticing that when I normally spot something like that easily. This is why your the champion and I'm not. Well done.

[@sHillChannel]

When you did the empty rectangle, I had found the same 2 by using skyscraper on the 34/39 pairs.

[@catsloverobots68]

Great video!The techniques you've shown are really helpful!

[@busdriver1261]

Great explanation of the various techniques - thanks!

[@anilbansal4969]

This might be my favourite video you've done!

[@aliciabrillante]

Thank you for not guessing! This was really hard but I like that logic was always used to one day I will be able to spot these triangles and wings myself.

[@lukefisher7618]

Don't be sorry. I am learning so much and solving much harder puzzles than ever before. Thanks!

[@fraewn2617]

Please more technique videos, I learnt a lot from this. Bought your app and it is so much fun

[@bogbel1]

I now have a headache, but it was worth it. Had to keep pausing and rewinding to fully understand the logic, but I eventually got it. Great tutorial!

[@soulwarrior]

Thank you for the excellent explanations! I appreciate this a lot more than brute force solving and I really don't mind you missing an "obvious" insertion here or there... to me, it's much more helpful to understand the logic of the advanced techniques and this video delivered in spades! :-)

[@traog2445]

I got it down to the 17 remaining squares easily enough then was stuck, I'd never seen the ideas you used to get beyond that point, interesting definitely somethings to be watching for.

[@tlvision1478]

That was great. Wonderful logic...much better than guess-and-error technique.

[@SiFuJasper]

Going through these videos has allowed me to solve expert level Sudoku on my app without help half the time now. I used to have to hit the help button often. Easy thru Hard are solvable without help, but the Expert level ones are tricky. I am finally making progress.

[@janetlohmeyer123]

Newbie, so I love that you go slowly, I can keep up with you that way. Thank you.

[@brendanmorales4504]

What a great solve, down to the last logic line to crack it!

[@ronaldkoh5281]

Super excellent illustration, all pure logical explanation, a great piece of sudoku solving for reference. Thank you very much.

[@JustJohnny666]

this puzzle was insane! so many logic ways of doing this that i can't. this one scared me

[@SUBHRAJYOTIMANDALmaysuj]

Highly helpful. Thanks

[@fingerling1231]

Glad you talked through these techniques in this video. A lot of them are things I've recognised as useful when doing solves but not being able to say why are take advantage of the patterns like you did here. Now that I'm more conscious of how to utilise such restrictions, it should improve my solving. Thank you :)

[@goldenera7090]

wow really enjoyed that one. thanks Simon

[@mateusquintana8658]

Amazing video! Thanks and keep up The good work!

[@amethystjean1744]

THank you learned y wing, skyscraper and empty rectangle for the first time!

[@havardgraff]

I actually coined the terms skyscraper and empty rectangle in what seems like a lifetime ago now... Super cool (and a bit surreal) to see them still being used :)

[@edgechill]

I have a headache! But s good one. You explain x and y and rectangle better than anyone else. Thanks.

[@davidmason1919]

Brilliant, these videos have helped me no end. Thanks 👍

[@soccerguru37]

Great video! I'm newer to the channel and it was definitely helpful!

[@freethinker3693]

my head hurts so much while watching the video, but glad that I caught a glimpse of the technique you were trying to explain.

[@jordancummings4639]

I got stuck on this puzzle with the exact arrangement of numbers you had just before explaining the "empty rectangle" logic around the 16:30 mark. That is a clever trick. I'll try to remember it. Thanks for the video!

[@worcesterexchange554]

Me too!

[@richard3765]

Great video, thanks for sharing.

[@JD-ee4df]

Beautiful

[@jrbr549]

There are some good tips that I've learned. But I was screaming at the screen because of that 179 triplet in row 8 that made R8C6 a 5.

[@leporid257]

or that he didn't pencil in r7c6 🙈

[@angelmendez-rivera351]

Yes, this happens in every video. Simon is better than most at using logic to make breakthroughs whenever he has hit a stop in the puzzle, but when it comes to the simpler things, such as tidying up his pencil marks and scanning the grid, then he performs much worse, possibly worse than the average person. Not that I am hating, though. It can be irritating to watch for those moments, but the videos are still entertaining enough for me to always come back for more.

[@hanspeterpitsch]

He even writes in all the candidates in r8 and and doesn't notice the 5 can only be in one cell :D

[@windybeach2184]

Even when working at this ‘slower’ pace for us, he’s constantly scanning and calculating the best next move. It’s easier for us as viewers to spot the more obvious things while we watch him work on the harder ones.

[@jonnybolton4659]

The 3 that is removed from the empty rectangle can be removed much earlier as soon as the 4 x-wing is found - the 34 pairs used in the x-wing also form another skyscraper on 3s with the 39 pairs that formed the skyscraper on 9s (that is, the 34, 39 and 49 pairs all communicate together to form x-wings/skyscrapers on all three numbers) and this skyscraper removes the 3

[@windybeach2184]

This was very helpful, thank you. I have been watching your newer videos but came back to some oldies to familiarise myself with these techniques. I can’t always spot where and when to use them but the app is helpful for highlighting digits so I can look for patterns. I still feel like I use a bit of trial & error but my game has improved a lot already and I was able to solve this one myself in decent time.

[@ilive4livemusic]

Thanks. I like the way you talk through the logic. Very helpful. I still struggle to find the empty, rectangles etc and to remember how to capitalise on them. The more times I watch you, the more it sinks in. Hadn’t heard of skyscrapers before.

[@titushui]

Another name for it is sashimi x-wing

[@ragnkja]

I don’t mind the longer “as live” sudoku videos, since the logic is always interesting

[@joshuanorthey2026]

Great job. That was a tricky one!

[@gregorymorse8423]

For me, that was the best not the worst way. The skyscraper technique, Y wing and and rectangle techniques are so much more intriguing than simpler logic. A lot of us who want to crack the hardest puzzles love being shown the harder logic tricks

[@EndlessMystify]

I feel very slow to the party, but this video served as a great explanation on how to use the various solving methods. Thanks a bunch for that ^^

[@leoncarpenter958]

yes thank you that was helpful.

[@thommartin4047]

Very well done! I have found a love for Sudoku and I have gotten pretty good at solving expert level puzzles but want to be bettter so decided to watch your videos. What’s weird is I have been using some of these techniques and not even realizing that they had a name. The skyscraper still has me a bit confused. Also by watching your videos I now know how it feels to see something and be yelling at the video. After you locked in the 3/4 in row 8 I solved the 5’s and the rest of the video I was trying to tell you “You’re missing the 5’s!” 😂

[@ozertamer210]

I have developped a notation for sudoku to make Simon'ss work easier. This is not guide for tricks but text mode of tricks found by sudoku lovers. This is just to make understanding the tricks easier. KEYS: Capital letters show BOXES, numbers show ROWS, small letters show columns.

[@willybouchentouf]

i learn much, thanks!

[@nicokuhne3255]

that was great!

[@Mlynoph]

Thanks this will help me alot.

[@marykosanke5431]

Wow, I'm new to Sudoku so this was a lot to take in. Two things I want to learn more about is the hidden singles and the concept of "what cell sees two other cells".

[@kaustin6969]

A cell sees all of the cells in the column, all of the cells in the row, and [which is important] all of the cells in the same block.

[@nathangarciamuro]

My gosh. I thought I could solve it!!! The techniques you have used are quite complicated. I can say I lower my level to medium and a little high sudoku solver. The y-wing and the skyscraper and empty rectangles techniques are very hard to understand and to spot on

[@JustFun-iz9rf]

Thank you

[@danielpimienta7388]

Feel proud that I got 2 of the fives before he did just before he blew my mind with the empty rectangle shenanigans

[@viodragon974]

If you get your videos in between 20 and 30 minutes, you are doing great. I enjoy watching the logic being played out.

[@igoretski]

14:16 Actually the X-wing with the 4s in rows 5 and 8, gives you some information about the 4s in row 4 and 7, where they now can only be in column 2 and 8 forming another X-wing. And also you have now exactly 2 positons for the 4s in boxes 4,6,7 and 9, which according your notation, you could pencil mark. At 19:35 you would immediately notice the position of the 4s in box 6 and 7 .

[@soundcrank6214]

Hey, love the videoss! Just a thought I saw someone mention before which I agree with big. You should get a dedicated mic for these. I'm a sound engineer, and I would recommend the Blue Yeti USB mic. Cheap and robust and has great clarity for the price :)

[@Untoldanimations]

Sound Crank For some reason my blue yeti isn't working at all with my laptop. I've tried it with another computer. It works with that one, but on my laptop the audio comes through all chopped up, if it's picked up at all. Have you dealt with this before?

[@WwortelHD]

I was hoping a sound engineer would know that the Blue Yeti isn't that great of an option. Rode or something along it would be a far superior option, even a cheaper microphone if it has XLR :)

[@soundcrank6214]

@@WwortelHD Honestly, the difference is negligible for this usecase scenario. For the cost of one, it's rated the number one podcast mic for a reason. Personally, I use a blue baby bottle, but not everyone has $360 spare laying around for a good mic lol

[@eamonnconnolly5245]

Hello there! I do enjoy your presentations which are, indeed, informative. As an aside may I comment that you use the word “solve” when in fact you should, if you wish to be correct, use the word “solution”. “Solve” is the verb whilst “solution” is the noun. As an example, incorporating both: I solve a problem by finding the solution. English is such a nice language and much richer than, for example, “American”. Perhaps we should try to stay alert to any external influence which might otherwise lead us to lose proficiency in our own language! All the best and keep up the very interesting Sudoku videos.

[@richardfarrer5616]

When you demonstrated the first empty rectangle, there was also an x-wing available in columns 2 & 8 on threes.

[@HULKEN1UP]

Easier to spot also and it gives you the same 2 in block 1

[@remigregoire2219]

You know what, good call on the new mike :-).

[@lochblade4573]

I enjoyed this video, this puzzle in particular has a lot of interesting techniques used. I love logic problems like these and I do them for fun, I've picked up some interesting tips in doing sudokus as well, this puzzle is great for teaching all the techniques listed. I think due to the limitation of the software used here you might have missed out on some stuff by having to remove some of your notations. I found a few interesting interactions on the puzzle, and one may help showcase another technique. At roughly the 13 minute mark you mentioned the X wing on the 4s in column 3 & 7, I had a few extra pencil marks having not cleared my notation and finding a hidden triple in box 9 after the 2 was entered as the 3, 4, & 5 are blocked from the outer edge by row 9 and column 9. I looked at the 4s and noticed the remaining locations formed an odd pattern, similar to crosshairs on certain gun scopes, and the X wing lined up with all the bottoms of the crosshairs, so I checked the top ends of the crosshairs and found another X wing in column 2 & 8, and all of these points interact with the other X wing, as each wing winds up in the same box, not entirely sure what this technique is called, of if it's just a variant of overlapped x wings. I think the quickest way to finish the puzzle once you get to the 23 minute mark is, a y wing or something located at row 7 column 4 dealing with a 1-7-9 triple, whatever digit placed in r6c4 has to appear in r7c6, which eliminates both 1 and 9 from r7c3 leaving a naked single cracking the puzzle.

[@2236UmbrellaCorp]

That was neat.

[@chrisguard696]

I appreciate the explanation of skyscrapers and empty rectangles, they aren't patterns I'm good at identifying or using to solve my puzzles.

[@nihatbekiroglu8004]

I'm not sure if this would have sped up the process, but at 12:30 there was also a 79 -179 - 179 triple in R8 along with the 43-43 matching pair which would give you the 5 in R8C6 earlier in the puzzle...

[@tiotito31]

23:43 He goes into empty rectangle, but an easier logic principle is skyscraper on the ones in row 4 and row 8

[@angelmendez-rivera351]

Yes, but this would have made the video less instructive, which I believe is actually the point of the video.

[@mrsulaman9901]

16:45 there is also an empty rectangle of 3s in the top three rows. This would eliminate the 3 in the bottom right of the first block and the 3 in the bottom middle of the third block.

[@kenthemaster]

I believe the explanation of the skyscraper is a bit off. The 9 can also appear in both R1C2 and R5C3, thus this is different from an X-wing situation. The crucial argument is that at least one of these two cells need to contain a 9, so the logic still holds that any cell that sees both these cells cannot also contain a 9.

[@brandonsheumaker2673]

I completely agree. The skyscraper comment at 9:10 is incorrect. It's possible for A2 and E3 to BOTH be a 9. It's similar to an X-Wing, but not. It's actually closer in logic to a Y-wing. One of the two "tops" of the skyscraper (A2 and E3 in this case) must be a 9, so no other cell that can "see" both of the tops can be a 9. Is this guy really a World Sudoku Champion? And he doesn't know that very simple piece of logic? I'm aghast.

[@angelmendez-rivera351]

@@brandonsheumaker2673 Cut him some slack. I am sure he merely misspoke. Constructive criticism is fair, but being an asshole as you are being is not fair. I would love to see you solve the hardest puzzles this channel and perform better than him, or even more convincing would be to see you make a channel and upload the same puzzles and provide objectively better and flawless explanations in every single instance with the same upload rate as the channel. If you can do that, then you are totally justified in being an arrogant asshole, although you would still be an asshole.

[@angelmendez-rivera351]

@@brandonsheumaker2673 Also, he was a world champion in his prime, not currently, so your loaded question is moot.

[@brandonsheumaker2673]

@@angelmendez-rivera351 Whether I'm an @$$hole or not is also moot. Read the comments: lots of people watch this channel to learn tips and tricks of high-level solving (myself included). Maybe he misspoke, yes, but passing off incorrect logic as valid (and not correcting it) is a disservice to the viewers who are trying to learn and should be called out for the inaccuracy that it is by those viewers who can spot it. My second-to-final comment was, I admit, below the belt. My last was not. I'm still aghast.

[@alienrenders]

Glad to know I'm not the only one who misses obvious triples for over 20 minutes.

[@ElanorKella]

What sort of sorcery is this? I feel like I've unlocked a secret knowledge. Thank you for showing this

[@SudokuGuy]

Great work. The elimination of snyder notation to avoid too much clutter. Does this limit your solving ablilty in any way.

[@DiMono]

The empty rectangle around the 18 minute mark could also be resolved via a second skyscraper on 3s in rows 8 and 1

[@sam3oq980]

I really enjoyed this. What I always do when the basic techniques didn't yield anything was just brute forcing it: "there are two options, if this goes here then ...(chain that is way too long) CONTRADICTION. Ah fuck the other option gives me nothing of value...". I didn't know about Y-Wings, Skyscrapers or Empty Rectangles. Thanks for that! It's very informative.

[@Cube__TV]

Interestingly at 16:30 I used a skyscraper to eliminate the 3 candidate from R3C3. The skyscraper is R18C7 for the base and R1C2 + R8C3 as the roof. This makes the same elimination as your empty rectangle. =)

[@zxzxmatheus]

yeah, i learned a lot from this

[@zxzxmatheus]

i still suck tho, need practive

[@yanmich]

I solved it using brute force after reaching a critical point, which is not entirely satisfying... this video showed me what to do... with a lot more practicing I will be able to do it on my own I guess.... thanks a lot!!!

[@Finsirith]

"My brain's not clever enough to do it quickly," he says. Well, my brain's not clever enough to do it AT ALL!

[@MegaJotie]

sick

[@pepshaven6520]

That was hard but once you boil it down, in the end row 7 & 8 can only lack a 7 1 9 which means colum 7 8 on row 9 can only be a 1 or a 6 and that unlocks the whole thing.

[@olliehopnoodle4628]

Persons reading the comments. Do you consider this BRUTE FORCE? At 22:45 he had penciled in all of the remaining boxes. He even comments he doesn't want to use 'Brute force' to finish the puzzle. He then goes on to find the empty rectangle and Y wing etc. I agree this is not a use of brute force since it still used logic even though all of the pencils were in. To me, brute force would be to guess a value on a pair and see if it works. THOUGHTS?

[@TheJameslehr]

Good question! VVhat is the minimal number of digits that can be placed in a Sudoku grid to make it a functional (but extremely difficult) puzzle to try to solve? Also been solving SUDOKU for Four Decades novv as i did see this puzzle make a debut in a DELL CROSSVVORD Puzzle Magazine in 1979.

[@igoretski]

15:00 There is a skyscraper with the 3s in rows 1 and 8. (Similar to the earlier skyscraper with the 9's in rows 1 and 4). Both cases together remove 9 and 3 from r3c3, which now must be a 2.

[@igoretski]

You (Simon) get to the same result looking at 3s with the empty rectangle in box 7 and the 2 restricted 3s in column 8. Surprisingly you could also look at the empty rectangle in box 3, which connects with the 34 pair in row 8. Again, also prooving that r3c3 can't be 3. Summarized: The 3 in r3c3 really had no chance.

[@leojf3828]

I'm impressed. There was a Master Sudokuist that could solve five hard puzzles in < twenty minutes. Might this be one of you Folks?