The rules of skyscrapers
Skyscrapers (also called towers) is a logic puzzle where you place building heights 1 through N into an N×N grid — here 4×4, 5×5 or 6×6. Every row and every column must contain each height exactly once, and the numbers around the edge say how many buildings are visible from that side. Every puzzle has exactly one solution.
The five rules
- Place a building of height 1 to N in every cell, where N is the grid size.
- Every row must contain each height 1 to N exactly once.
- Every column must contain each height 1 to N exactly once.
- Each clue around the edge gives the number of buildings visible from that side: the first building is always visible, and every taller building hides the shorter ones behind it.
- There is exactly one solution, reachable by logic.
How to read the grid
The numbers around the border are the clues. Imagine standing at the edge of the grid and looking straight across the row or column. The clue tells you how many buildings you can see — and a taller building hides everything behind it.
How visibility works
Look along a line of heights from the side the clue sits on. The first building is always visible. From then on, a building is only visible if it is taller than every building before it. For example, heights 2, 4, 1, 3 show two buildings: the 2, then the 4 (the 1 and 3 are hidden behind the 4). The same line viewed from the other end — 3, 1, 4, 2 — shows three buildings: 3, then 4, then 2.
One more thing: rows and columns
Every row and every column is a complete set of heights 1 to N, like a sudoku line. The edge clues are your only way to order them, so a clue of 1 (the tallest building sits right at the edge) or a clue of N (the line rises in perfect order 1, 2, 3 … N) is often where a puzzle unlocks.