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An entry in Fortnightly Topic Challenge #47: "Wacky Sudokus"

Other puzzles in this series



Welcome to the tenth puzzle in this series! For more information about the series, see the first puzzle and the introduction. Enjoy!


             enter image description here

9 really blocks the view yknow...

Google Sheets link


RULES:

  • Normal Sudoku rules apply
  • Each digit can be seen as a 'skyscraper', with as many floors as the number
    • E.g. A cell with a 4 could be seen as a 4 story skyscraper
  • The number on the outside of the grid is how many skyscrapers that row or column can 'see'. A larger digit will block any smaller digits behind it from view

Visual representation of the rules:

enter image description here


Hopefully that makes sense, if not I can try and clarify further!

This is one of my favourite wacky sudokus, and also this is one of the harder ones, so if a full explanation is possible please give it!

I'm especially interested in the logic people find for this sudoku...

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  • $\begingroup$ Really Interesting, impressed by the variety of puzzles you have made !! $\endgroup$ – Anonymous Jan 19 at 17:51
  • $\begingroup$ @Anonymous yeah this is my favourite of all the wacky ones :) I wish I could take credit, but sadly none of these are original ideas, and I have seen them all before, but I wanted to make my own to showcase my favourites here! $\endgroup$ – Beastly Gerbil Jan 19 at 18:03
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    $\begingroup$ This one was awesome! Super enjoyable :-) $\endgroup$ – Jeremy Dover Jan 19 at 18:38
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    $\begingroup$ There are redundant clues here, for example the "2" clues in row 9 and column 9 are obviously unnecessary. Skyscraper sudokus are more fun with the minimum number of clues, not every possible clue. $\endgroup$ – alephzero Jan 20 at 2:05
  • $\begingroup$ @alephzero oh do you mean on the outside? That would be interesting, the only ones I’ve ever seen have had all the outside clues filled in, so I copied that format when making this. There’s no doubt this could be harder, but these are mostly aimed as a showcase of these types of sudokus, so the aim is more light hearted fun than difficulty, though I tried making most as hard as I could :) $\endgroup$ – Beastly Gerbil Jan 20 at 2:30
9
+100
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COMPLETED GRID

Grid

REASONING

Any Skyscraper view with a 1 must have 9 on its edge, giving us four 9s along the edges, and lets us fill in all of the 9s. In the first column looking down, there are only two buildings seen, but the 8 cannot be on the other side of the 9, so it must be in the first row. Continuing in this column, the only remaining numbers to be placed are 1, 4, 6 and 7, and all but 7 are barred from row 2. In row 8, R8C1 cannot be 6, which is blocked. It also cannot be 4: there are four buildings seen, which must be R8C1-4. If R8C1 were 4, R8C2-3 would have to be between 4 and 9, but 5, 6, and 8 are all barred, leaving 7 the only possibility. Thus R8C1 must be 1.

Continuing in the lower left square, 7 must be in R8-9C3 by Sudoku rules, but it cannot be in R9 because of the 4 buildings seen up in column 3, so R8C3 is 7. Now the 6 in this square must be in R7C1-2, but if it were in R7C2, R7C1 would be 4, showing 4 buildings from the left. This lets us fill in the entire first column. The grid thus far:

Progress

Looking up top:

In the first row, 7 is blocked from the upper left square, and cannot be in the upper right square since we would then see three buildings from the right. So R1C5 is 7. The 2 building view looking down column 5 forces the 8 to be in R9C5, with Sudoku rules forcing R8C7 to be 8 as well. Back to the upper right square, its 8 has to be in R2-3C8, but it cannot be in row 3 since we would only see 3 buildings from the right. Sudoku rules let us finish row 2.

Some miscellaneous deductions come now. In row 3, since we only see two buildings from the left, R3C2 has to be 1. In column 4, the only place a 7 can go is in R9. In the top row, the two missing cells in R1 are 3 and 4, meaning the missing cells in the upper right square are 1 and 2, and their positions are forced. Column 5 only needs 1, 4 and 6, and their positions are forced too. The grid thus far:

Progress

At the bottom:

The 6 in the lower middle square is forced to be in R9C6. This leaves the possible values for R9C8 as 1, 3 and 4, which are all less than 6; thus the 7 in column 8 must be in R3C7 to see only three buildings from the bottom. This forces the 7 in row 7 to be in R7C9 by Sudoku rules, and R5C7 finishes the placement of the 7s.

Looking in row 5 from the right, to have 5 buildings seen we are now forced to have R5C6 to be 8, which lets us finish the placement of the 8s in R6C2 and R3C4, the latter of which forces R3C6 to be 4. Sudoku logic in column 6 forces R4C6 to be 3. The grid thus far:

Progress

Finishing up:

By Sudoku rules in column 2, the 6 must be in R5C2, the placement of which forces the entire middle left square. In the bottom row we cannot have 1 in R9C9, since we would see 5 buildings from the right, so R9C8 must be 1. We complete the placement of 1s with R5C9. This forces R6C9 to be 2, which in turn forces R4C4 to be 2. The rest is just Sudoku fill-ins.

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  • $\begingroup$ Just beat me to it! It matches what I have, so +1! $\endgroup$ – samm82 Jan 19 at 18:40
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    $\begingroup$ Great answer once again!! This is my favourite variant, so I'm glad you enjoyed! Unlucky @samm82, there's still 4 more incoming for you to try :P $\endgroup$ – Beastly Gerbil Jan 19 at 18:45
  • $\begingroup$ Added a bounty for this answer, in my opinion, its the best in this mini series, adn thoroughly deserved! $\endgroup$ – Beastly Gerbil Jan 23 at 20:00
  • $\begingroup$ @BeastlyGerbil Not needed...the pleasure was in solving a great series of puzzles! But appreciated very much :-) $\endgroup$ – Jeremy Dover Jan 23 at 20:02

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