145
Techniques · Hard
Skyscraper
A digit has exactly two places in each of two rows. One end of each row lines up in the same column, the other ends do not. The two lined-up cells share a column, so at most one of them holds the digit, and the other row then has it at its free end. At least one free end holds the digit, so any cell that sees both free ends can lose it. It also works with columns.
How to spot it
It looks like an X-Wing with one leg out of line. Find two rows with the digit in two places each, sharing one column. Remove the digit from cells that see both loose ends.
Example
3
15
4589
49
158
2
6
7
2
145
7
345
6
135
13
8
9
9
6
8
237
237
1237
5
4
13
8
125
9
257
27
4
167
3
156
6
25
35
1
237
9
4
257
8
4
7
135
6
8
235
9
25
15
5
3
4
79
1
6
8
79
2
7
9
26
238
5
238
36
1
4
1
8
26
23479
49
237
367
579
356
In rows 5 and 7, 7 has exactly two places each and column 8 links them, so r5c5 or r7c4 must be 7 and 7 can be removed from cells that see both (Skyscraper).
the pattern cells that lose a candidate (crossed out)