Tutorial #75. The skyscraper A detailed look.

#sudoku #learn Sudoku #Sudoku guy
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The skyscraper takes time to spot but can be very valuable in eliminating small numbers.
An understanding of strong (conjugate pairs) and weak links is important.
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Shehu Mayaki sent me this summary. Thanks Shehu
SUDOKU SKYSCRAPER TECHNIQUE
1) 1 Candidate forming a conjugate pair (i.e: only 2 cells in a row or column) in 4 separate cells which lie in 4 different blocks
2) The 4 cells are connected by 2 strong links (conjugate pair) and 2 weak links on any 2 opposite sides and must lie parallel to each other
3) The links must be in the order of strong - weak - strong
4) One side of the resultant parallelogram must be slanted while the remaining sides are flat (the 2 points of the slant must be on 2 rows or 2 columns)
5) The slanted side is said to be the roof of the skyscraper, while the opposite side of the slant is the floor
6) The higher side of the slant (roof) forms one corner while the lower side of the slant (roof) forms another corner (Note: no link, either strong or weak, between the 2 ends of the roof!)
7) The two ends of the floor form the other other 2 corners
8) There are 2 types of eliminations that can be made: a) on the roof of the skyscraper and b) on the skyscraper walls using X-wing diagonals
9) Eliminations on the roof will be the skyscraper candidates that see both ends of the roof (i.e. the candidates on the same row or column of the roof and also in the same block as the lower end of the roof)
10) The second set of eliminations will be those aligned with the diagonals (X-wings) of the skyscraper candidate, using the X-wing rule!
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[@RonMaxfield]

Robin, have you ever been a school teacher. You appear to me as a math, school teacher. If you were a teacher at one time you had to be the best teacher in the entire School. You are witty, you get the point across very well and you have the ability to hold our attention. Thank you very much for all these videos they have helped me immensely. I am hooked on Sudoku. I can't go to sleep at night without playing at least three games of Sudoku. Thank you! 🤗😀🤗

[@SudokuGuy]

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[@SmartHobbies]

Great video Robin. I love the shoutout to the Swami. You both have taught me so much about Sudoku. One note of caution about skyscrapers. The strong weak strong link relationship only tells us that at least one of the roofs is true so we can make eliminations, but they could both be true as well. You seem to imply at the beginning that you can assume that one of base numbers has to be true so we can make eliminations along the base column or row and that’s not completely accurate. In your example with the 3’s in row 7, we could only make eliminations along row 7 after seeing the effect the roof had on the 3’s in the upper rows, not before. I hope that makes sense.

[@SudokuGuy]

Thank you for your comment. Yes you have a point and i should have mentioned this.

[@SoRTs6233]

I was working on a puzzle and I knew there was a skyscraper there but I didn't know what to do. After this tutorial, I went back to the puzzle, used your technique and got it solved! Thanks Robin, great work. Cheers

[@SudokuGuy]

So pleased to hear that....congratulations. Please tell others about my site.

[@bookaholic1431]

Thank you so Much for the helpful tutorials, Mr. Robin!🙏

[@SudokuGuy]

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[@alwyalbiansyah]

best teacher i've ever had

[@SudokuGuy]

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[@shehum]

Aw! Wow! I've finally added skyscraper to my repertoire of solving techniques! Not that I have many to begin with! Apart from the basics, I only have X-wings and Unique Rectangles (URs) to work with. But now thanks to this tutorial, Robin, I have another technique. Can't wait to recognise and try it out. See my notes from this tutorial: SUDOKU SKYSCRAPER TECHNIQUE 1) 1 Candidate forming a conjugate pair (i.e: only 2 cells in a row or column) in 4 separate cells which lie in 4 different blocks 2) The 4 cells are connected by 2 strong links (conjugate pair) and 2 weak links on any 2 opposite sides and must lie parallel to each other 3) The links must be in the order of strong - weak - strong 4) One side of the resultant parallelogram must be slanted while the remaining sides are flat (the 2 points of the slant must be on 2 rows or 2 columns) 5) The slanted side is said to be the roof of the skyscraper, while the opposite side of the slant is the floor 6) The higher side of the slant (roof) forms one corner while the lower side of the slant (roof) forms another corner (Note: no link, either strong or weak, between the 2 ends of the roof!) 7) The two ends of the floor form the other other 2 corners 8) There are 2 types of eliminations that can be made: a) on the roof of the skyscraper and b) on the skyscraper walls using X-wing diagonals 9) Eliminations on the roof will be the skyscraper candidates that see both ends of the roof (i.e. the candidates on the same row or column of the roof and also in the same block as the lower end of the roof) 10) The second set of eliminations will be those aligned with the diagonals (X-wings) of the skyscraper candidate, using the X-wing rule! There! Hope I made sense!!

[@SudokuGuy]

FANTASTIC summary. I will add it to the description underneath the video and give you credit.

[@shehum]

@@SudokuGuy Wow you've made my day, Mr. Robin! Thanks a lot for also making me know that I'm on the right track.

[@wood_pecker_]

@@SudokuGuy you are so kind sir ❤️❤️❤️

[@povrtsux1]

LOVE IT. GOD BLESS YOU FOR ALL YOUR HELP !!!

[@SudokuGuy]

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[@DuyNguyen-pb4pw]

This just singlehandedly solved the puzzle i was stuck on. Thank you so much for showing this technique!

[@SudokuGuy]

Glad it helped! Duy. So glad you found my site."the most popular site on line to learn sudoku" Please share with others, subscribe and click the bell by the subscribe button. (It’s FREE) Have fun as you learn step by step how to solve. Below is my home page with all the videos listed. kzbin.info/door/d8JaOdfEWcJOtwG6YayW0w

[@initiativeplaytherapy88]

I almost never see classic X wings, but I see this pattern. All. The. Time! Definitely going to use this one. Thanks.

[@SudokuGuy]

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[@DanaHuseby1017]

Thank you for taking the time to explain the process so clearly!! 😁

[@SudokuGuy]

You are so welcome! hang in there, You can do it. master one level at a time. Each video will take you a step further and revise what has already been covered, particularly procedure.

[@terrybolerjack197]

Thank you Robin! I always find value in your videos!!

[@SudokuGuy]

You are so welcome!. Thank you for your support. And thanks for telling others. Roibn

[@cakemashers1816]

Thank you! I didn’t know about this technique. It’s very helpful as it seems to available quite often. You have a great aptitude for teaching and with your winning personality, you remind me of the Bob Ross of Sudoku. You are beloved in our household.

[@SudokuGuy]

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[@danivaljean9073]

divino, genio, te adoro! Gracias por tu dedicación!!!!

[@SudokuGuy]

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[@FaithApologetics2.0]

Robin sir is the best sudoku teacher in the world I think Sudoku guy is amazing If I press a video of sudoku guy I can't press back until the video end Fabulous work May God bless you with good health and strength 🔥❤

[@SudokuGuy]

Gee!!!! thanks....you have made my day!!

[@FaithApologetics2.0]

@@SudokuGuy yee 😍❤

[@gardenbee583]

You are a great teacher, Robin Sir.😀🙏

[@SudokuGuy]

Wow, thank you

[@prabhattomar4587]

Thanks for explaining and clearing doubts. Sky scrapper is an excellent method to solve the puzzle.

[@SudokuGuy]

Happy to help. Prahbat. So glad you found my site. “the most popular site online to learn sudoku” Please share with others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step to solve. You will find all of my videos below. kzbin.info

[@user-gi8fs6xl5o]

Saving in my playlist, I will watch after working hours

[@SudokuGuy]

Great Z. Sometimes watching more than once helps too.

[@iamshemyo6563]

Thank you so much. This technique has helped me to think better when solving the puzzle.

[@SudokuGuy]

Glad it helped lanshe. So glad you found my site. “the most popular site online to learn sudoku” Please share with others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step to solve. You will find all of my videos below. www.sudokuguy.com or kzbin.info

[@kskaliprasadkotagal6468]

Thank you for your efforts teach. Today I am very happy and clear about skyscraper. Thank you again

[@SudokuGuy]

You are most welcome

[@78tag]

In the upside-down roof, you stated that the 3 "inside the house" couldn't see the 3 in the corner of the roof (because it is in the same block) so it couldn't be eliminated. Did you mean to say it couldn't be eliminated because it couldn't also see the other corner that wasn't in the same block? I'm not trying to be a wise guy here - I am finally at the point where I can sometimes use the X-Wing to solve puzzles that can't be solved by pure elimination. I only halfway understand the elimination process of the X-Wing and your explanation of the Skyscraper is really helping my progress. Thanks much. EDIT: when I went back to that explanation, I caught the part about it "needing to be outside the block AND it can't see the bottom corner because it isn't in the same block (meaning it isn't in the same row/column). I was going to delete this comment when I made that realization but then I thought maybe some else might get something from my query.

[@SudokuGuy]

Thanks for sharing.

[@a_son_of_light]

Question for Robin: Reference: time mark 14:07 to 14:22 My thinking was as follows: The 3 inside the building (R4C6) CAN "see" the 3 in the left (bottom) corner of the roof (R4C4) (because it's in the same house), but it CANNOT "see" the 3 in the right (top) corner of the roof (because it's NOT in the same house), so it CANNOT be eliminated. (same house = common row, column, or block). Any 3 in this puzzle that can interact with the skyscraper would have to be able to see both corner-of-the-roof 3's or corner-of-the-floor 3's in order to be eliminated. It's two different ways of looking at it, but I don't understand why one would assume the 3 in R4C4 to be real rather than the 3 in R4C6. If R4C6 is the real 3, it's a very different outcome, so shouldn't that possibility have been included and explained in the video? I'm confused. I would appreciate any corrections to my understanding. Thank you.

[@78tag]

@@SudokuGuy - I am leaving these conversations now. The time I was spending on puzzles is consumed with thought on what Biden/Obama are doing to the country and what, if anything, we can do about it. It was nice knowin' ya.

[@lfavila50]

Very Nice. Thank you!!!!!

[@SudokuGuy]

Thank you too! and for your support. Luiz

[@itsbouquet5276]

Great Teacher Ever!!😊🥳💖

[@SudokuGuy]

Thank you! 😃 So glad you found my site. “the most popular site online to learn sudoku” Please share with others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step to solve. You will find all of my videos below. kzbin.info

[@jamesgoacher1606]

That was an interesting and absorbing video. I accumulated questions as you wen along (of course) and you answered as you progressed. The first thing that I queried that became clearer later way when you said a candidate was not I paused the vid and looked at it as if it was, that type of thing etc. The last puzzle was good and I am glad you showed it. I first saw 3 as a possibility then the 8s. Pleased with myself. The remaining question that I have to ask is in which order do you apply these "rules" there were a couple of places where the solution was evident in another, simpler manner. and I tend to avoid cluttering up the puzzle with candidates until the more straightforward methods are done. Fot instance I slice and dice with the numbers 1-9 first, then I start with the more creative ways.

[@SudokuGuy]

Hello James. Yes I have a step by step procedure. however If I see something that can be useful re getting another number or more I will use it. Beginners need to learn a procedure. It is the teacher in me! You appear to be progressing and that is great. congratulations. Robin.

[@jamesgoacher1606]

@@SudokuGuy Oh Dear! I have been doing them since they started to appear in The Guardian some twenty years ago I suppose. They should be included on the list of Class-A Drugs. I have fix of about half a dozen each morning half/half Classical/Killer although I do not get very far with the Killer past Moderate. To be honest the solving "Rules" for 'Killer' have never gotten fully into my head. Even an 'Easy' one can take an hour but strangely if I break off for some reason at a stuck phase when I come back it sort of leaps out. It must be difficult to do the teaching videos I assume becase your inner head is a dozen jumps ahead of your Marker Pen. :-)

[@niniacresiannjalagat5386]

You're so great sir!

[@SudokuGuy]

Thank you kindly! So glad you found my site. “the most popular site online to learn sudoku” Please share with others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step to solve. You will find all of my videos below. kzbin.info

[@GFlCh]

At 22:55, you've just placed the "Big-5" in the left corner of the Roof, and are getting ready to eliminate the "Small 5" of the "5/9" at the right corner of the roof at "Row-2/Column-8". Notice, there is also another "5/9" in the same row, at "Row-2/Column-9". But there are no "Strong-Links" that you usually draw in Red to represent the Walls of the Skyscraper. So, how did you choose the "5/9" in "Column-8" instead of "Column-9" for the right corner of the roof?

[@SudokuGuy]

I hope this helps. Yes your point is well taken, but this was a small section to show a technique.

[@junkmailfolder5600]

Great explanation professor! 🙂

[@SudokuGuy]

Happy to help! Love you name! So glad you found my site."the most popular site online to learn sudoku" Please tell others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step how to solve. You can view all of my videos here: kzbin.info/door/d8JaOdfEWcJOtwG6YayW0w sudokuguy.com

[@yousraben9417]

I finally understood it, thank you ❤️

[@SudokuGuy]

Glad it helped! You are on your way now to try harder puzzles. They get harder as you go up in numbers. However on the way I revise and introduce new techniques for solving Robin

[@amithaabeykoon7309]

thank you sir

[@SudokuGuy]

Most welcome. there is always something to learn. eh!

[@vitormonticelli405]

Can you apply skyscraper if the roofs are in different blocks? (For example, at 3:01 if the 8 that is on Row2 Column3 was on Row4 Column3 instead of Row)

[@SudokuGuy]

Yes you can providing the wall are parallel.

[@clinex3223]

Men you are always great thanx to you

[@SudokuGuy]

I appreciate that! clinex So glad you found my site. “the most popular site online to learn sudoku” Please share with others, subscribe (FREE) and click the bell by the subscribe button. Have fun as you learn step by step to solve. You will find all of my videos below. sudokuguy.com kzbin.info

[@AbdulMumin0]

You are AWESOME!

[@SudokuGuy]

You too!! Abdul You can do it...nothing like practice and looking at my tutorials and lessons. So glad you found my site. “the most popular site online to learn sudoku” Please share with others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step to solve. You will find all of my videos below. kzbin.info

[@osvaldobenavides5086]

Thanks!

[@SudokuGuy]

No problem! osvaldo.

[@saeed0x1]

love your videos 😍😍❤️❤️

[@SudokuGuy]

Thanks Lots to learn eh! So glad you found my site. “the most popular site online to learn sudoku” Please share with others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step to solve. You will find all of my videos below. www.sudokuguy.com

[@MrElBenno]

Hey Robin, another good video! Thank you! did u use the german word 'kaputt' for elimination? :D How do you know that, would interest me :D

[@SudokuGuy]

I studied German and my dad used to use this word.

[@MrElBenno]

Oh that is very interesting :D So i was right that you used this word, one of your funny thing, that makes me laughing :D

[@sgarcata]

Can the ends of the roof exist in the same block? the same shaft?

[@SudokuGuy]

Sorry no. The corners of the skyscraper are always in a different block Try looking at other tutorial/lessons on my site which cover the skyscraper. Robin

[@andrewan8855]

for the weak link how can we so sure that if one is not 8, other end of weak link must be? on the bottom row, can we have not 8 and not 8 for the weak link? where bottom row 8 is at other column? i am confused about it has to be a X wing. i mean there is a weak link.

[@SudokuGuy]

I suggest keep watching. Sorry Andrew. All the best. So glad you found my site."the most popular site online to learn sudoku" Please share with others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step how to solve. For a list of videos go here: kzbin.info/door/d8JaOdfEWcJOtwG6YayW0w sudokuguy.com

[@hannahjewell8363]

Where do u explain weak link surrogates?

[@SudokuGuy]

Go to my channel page sudokuguy.com and click on tutorials and scroll down to tutorial 68 and 70 This may help. Robin

[@GreenMeansGOF]

I don’t understand the X-Wing step. What is stopping both roof corners from being the candidate?

[@SudokuGuy]

I am not sure what you mean however in the sky scraper the roof must always be on a slant. Please le me know the min/sec in the video you are referring to.

[@GreenMeansGOF]

For example, at 17:36, why does row 4 column 5 have to be a 5? Why can’t row 4 column 9 be a 5?

[@dailydribble]

Gosh as a new player, just got a book and the first group of lessons is "shadows" and I think the book is wrong, being here goes: Multiple shadows grid 1-9 Hstrip and A-i V strip ok now told to put 1's in G-5 and D7 and the shadow will only leave i-9 for a 1 but I see i-9 and h-9 for a 1 what am I missing it is the same as no same number in the block or + ;) looked for your recent clip to ask

[@SudokuGuy]

Hello Deborah, I think you need to get another book as what you have seems to me to be very complicated.

[@dailydribble]

@@SudokuGuy thanks so such a prompt reply what a pleasure, yes what I don't understand is the shadow, and X in a cell and an empty cell (ugh) here is the properties: If a cell X is empty, then no number in the shadow of X can be entered into X, If a cell X contains a number , then that number cannot fill any other cell in the shadow if X, it seems alright but then tricky with what no number just pick any blank cell. Lucky I came across you channel, thank you so much Or ever heard of shadowing?

[@christopherjamescj1331]

25:08 why cant i assume that three can be in both the upper right block and upper middle block

[@SudokuGuy]

Column 2 is Ok but column 6 will not work as it has 3 cells with a small 3 which means it is not a strong link. I hope I have understood your question Robin

[@christopherjamescj1331]

​@SudokuGuy no i meant why cant there be 3 in column two and colum five

[@christopherjamescj1331]

4:42 why cant there be 8 in left lower block

[@noraromaguera4737]

Your like the sudoko god

[@SudokuGuy]

Really Thanks,

[@menjobleeko4135]

So you would have to find four blocks without that big number, or it wouldn't be there.

[@SudokuGuy]

Yes Thanks for sharing. Robin

[@christopherjamescj1331]

4:39 why are you assuming that the bottom left of sky scraper is the real 8

[@SudokuGuy]

Thanks for your question. The best way for me to explain is to ask you to look at tutorial #62 and #63. Also this is not a real puzzle but a demonstration of a technique Yes the base could be either one corner being an 8 ot the other corner being 8. It depends on What happens if this was a complete puzzle. Robin

[@shamabole7803]

I thought the top of the skyscraper had to hinge on CPs, But 235 isn't. 15:20

[@SudokuGuy]

CP's ??

[@shamabole7803]

@@SudokuGuy Conjugate pairs

[@SudokuGuy]

See my comment below. Thanks for your comment.

[@christopherjamescj1331]

Why cant hothbthebipper points of skyscraper be real sixes here, @11:45 . The elimination using roof is crystal clear but the one using diagnals seems unclear . U said for argument sake assume if it is a real six but it seems like u r ruling out the other possibility

[@SudokuGuy]

I suggest you look at my tutorials # 62 -3 as these show the diagonal of an Xwing. A skyscraper has similarities to an X wing.

[@austinbrian4082]

You can go ahead and throw that thang on 1.25x

[@SudokuGuy]

Not sure what you mean. Hang in there.

[@MrChrisdube]

You keep saying "if this became a real "pick a number" then the one in the same row or column can't be that same number.1 You never seem to specify how you know that number that you use hypothetically IS the actual number.

[@SudokuGuy]

This is deliberate. I am just explaining a rule. Hope this helps.

[@78tag]

He is just saying (to save the time solving the puzzle) that as you go you might narrow one of those corners to the one number you were looking for.

[@chiowastaken]

who still play sudoku in 2021 ?

[@SudokuGuy]

Me!!!! So glad you found my site. “the most popular site online to learn sudoku” Please share with others, subscribe and click the bell by the subscribe button. Have fun as you learn step by step to solve. You will find all of my videos below. kzbin.info

[@lory6605]

Where you ever a teacher?

[@SudokuGuy]

Yes it was my profession for 330 yrs.