GridWits
Easy tier Technique 2 of 21 Smart Hint: Skyscrapers and Skyscrapers+

Hidden Single

A height has only one possible cell left in this row or column, even though that cell has other candidates too.

How it works

  1. 1Instead of asking what a cell can be, ask where a HEIGHT can go. Hunt for the 4 in the second row.
  2. 2Column 1 already has its 4 at the top, column 3 has one in the third row, and column 4 has one at the bottom — three of the four cells are out.
  3. 3Only the second cell survives. It still lists other candidates, so it's no Naked Single — but the 4 has nowhere else in the row to live.
  4. 4Place the 4. This is the technique that keeps a board moving once the obvious cells run out.
4 1 2 3 1 2 4 1 2 3 1 2 3 4 4
  • Relationship — The arrow shows which cells support the deduction.
  • Conclusion — The final arrow lands beside the proved or ruled-out height.
Next in the ladder Clue of One →

A clue of 1 means the tallest building is visible right at that edge — place the max height there.