The New Sudoku Players' Forum

[Fortesque92]

I now have a fairly good understanding of how Skyscrapers work but I am still having trouble spotting them. Has anyone got any advice on spotting Skyscrapers?

[Leren]

Try practice. The following puzzles have Skyscrapers following singles. The code after the puzzle tells you the Skyscraper's digit and where to find it.

Code: Select all

...28.754.9.4.38............397..28.84......3.5.....7...8..1.9......5..23.6......  6 c69
...........19.2.6......679.9.2...6..37....95...5.....414...3..57.9.24......8.....  1 c69
2.......6.4.......5.7918........3.......8..1.7.3..9.....23.784..85...1..9......5.  2 c58
..56.8..33...5.....67..............1.82.145....6........45....77..96..1....1...2.  7 r15
....41...5.67.2..1.2........4.9....2..9.586436..........41....57...8.....5......9  8 r26
..9..35...627.....17...8.....6.....55.......3.93.8.2....72..6.9.....1..........8.  4 r26
.92.3.14737.....69......3....7......4....2......4..23..6..45....8.39...2....1.98.  8 r26
.23..49...5..1.4.....52......5.6.3.741.8....6.7.....................61..198.4.5..  3 c48
.865.........4...8.9...2.......1....4..7....59......1......5.63...18.9..65..9.8.4  6 r25
.1..9.......68..2.2...........35..9..7...98.3...2....4..316...54.8...1........7..  5 r25
....2.........1.8.7.5.649.34.7...8.......2..4........5.5...7.19.89..32..3.6......  6 r25
.3......4..67......79.4.2..36............5...7..4.23......2..96...374..1.2..5....  6 r36
..1.....9.8.9...32..2173....2.............27..148..6......9........5..6319...7...  4 r28

Leren

[denis_berthier]

All solved with 1 or 2 finned-X-Wings.
Is there a genuine one that can't be reduced to finned-X-Wings?

[Fortesque92]

[quote="Leren"]Try practice. The following puzzles have Skyscrapers following singles. The code after the puzzle tells you the Skyscraper's digit and where to find it.

Not sure how to read this, is it supposed to look like this?

https://ibb.co/X5qdLH5

[Hajime]

All solved with 1 or 2 finned-X-Wings.
Is there a genuine one that can't be reduced to finned-X-Wings?

I think a Skyscraper and a Finned X-wing are identical.... Isn't it ?

[denis_berthier]

All solved with 1 or 2 finned-X-Wings.
Is there a genuine one that can't be reduced to finned-X-Wings?

I think a Skyscraper and a Finned X-wing are identical.... Isn't it ?

As far as I know, a skyscraper involves 2 finned x-wings, at least if I believe Hodoku ("A Skyscraper is a simple pattern that occurs rather often in sudokus and can be easily spotted. It is nothing really new: A Skyscraper is a special form of Turbot Fish and it can be seen as two Sashimi X-Wings."): http://hodoku.sourceforge.net/en/tech_sdp.php#sk
But I'm not sure there's any "official" definition.

Leren, can you tell as more about this?

[Hajime]

I see. And according to the examples in http://hodoku.sourceforge.net/en/tech_fishfs.php#fbf2 the Finned X-wing has 3 candidate cells in a tower, what makes it not a Skyscraper.

[Leren]

You can read Hodoku's explanation of Skyscrapers here which does explain that they can be seen as two Sashimi finned X Wings.

If there is one leg with 3 cells I call it a grouped Skyscraper but maybe that's just my own terminology.

Fortesque92's image appears correct. Not quite sure why he can't see it direct. Maybe he is using a phone. Here is the first one in the list :

Code: Select all

*--------------------------------------*
| 1 6 3  | 2   8     9  | 7    5    4  |
| 7 9 25 | 4   56    3  | 8    26   1  |
| 4 8 25 | 1   567  b67 | 369  236 c69 |
|--------+--------------+--------------|
| 6 3 9  | 7   1     4  | 2    8    5  |
| 8 4 7  | 5   269  a26 | 19-6 1-6  3  |
| 2 5 1  | 3-6 39-6  8  | 4    7   d69 |
|--------+--------------+--------------|
| 5 2 8  | 36  4     1  | 36   9    7  |
| 9 7 4  | 8   36    5  | 136  136  2  |
| 3 1 6  | 9   27    27 | 5    4    8  |
*--------------------------------------*

Skyscraper : (6) r5c6 = r3c6 - r3c9 = (6) r6c9 => - 6 r5c78, r6c45; stte

All the examples were taken from Hodoku's exemplar list. I put the location codes in manually and found a mistake in the location code for this one, which I've corrected in my other post.

Leren

[Fortesque92]

You can read Hodoku's explanation of Skyscrapers here which does explain that they can be seen as two Sashimi finned X Wings.

Leren

Thank you, the Hudoku page is quite helpful!