The what-if technique says: suppose a square is one of its heights, and follow what that forces. If some square or line runs out of options, that height can’t go there. It’s the technique for when nothing simpler works anywhere.
This is the last of the Skyscrapers techniques. Each page shows its technique on the same 7×7 from the game, Hard level 1.
The rule
- Check that no simpler technique finds anything.
- Pick a square with two heights left, and suppose it’s one of them.
- Follow what that forces through the clues and the lines.
- If a square is left with no height, or a line with no ordering that matches its clues, cross that height out.
In a real puzzle
On the 7×7, it’s needed once, at step 16. Row 1, column 2 could be 3 or 4. Supposing 3, the clues and the lines run out of options. So it isn’t 3, and at step 17 it becomes a 4.
How often you’ll need it
Never on Easy or Medium, and on every Hard level, about 5 times each on average (4.9). On the 7×7 here it’s 1 of the 47 moves.