Skyscrapers: One Height Left

When a square’s row and column, and its notes, leave it only one height it could be, that’s its height. It’s the most used technique in Skyscrapers, just as in Sudoku.

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This is one of the Skyscrapers techniques. Each page shows its technique on the same 7×7 from the game, Hard level 1.

The rule

Pick an empty square.
Cross out every height already in its row and its column, and any its notes have ruled out.
If one height is left, write it in.

In a real puzzle

On the 7×7, it’s first needed at step 17, straight after a what-if. Row 1, column 2 could only be 3 or 4, and the what-if has just ruled out 3. One height left: 4.

Step 17: with the 3 ruled out, row 1, column 2 is 4.

How often you’ll need it

On every one of the game’s 150 levels, more than any other technique: 12.4 times per Easy level on average, 16.4 on Medium and 26.8 on Hard. It’s 26 of the 47 moves on the 7×7 here.

Next steps

Questions

How is this different from one place left?

One height left looks at a single square and asks which heights it could be. One place left looks at a single height and asks where in a row or column it could go. They find different moves, so use both.