Skyscraper Sudoku
Outside clues show how many 'buildings' are visible from that edge
Easy
Skyscraper Sudoku Easy
Medium
Skyscraper Sudoku Medium
Hard
Skyscraper Sudoku Hard
Expert
Skyscraper Sudoku Expert
What is Skyscraper Sudoku?
Skyscraper Sudoku imagines each digit as a building of that height. Clues outside the grid indicate how many buildings you can see looking from that edge inward — a taller building blocks all shorter buildings behind it. A clue of 1 means the first building must be a 9. A clue of 9 means the buildings are arranged in strictly increasing order (1,2,3,4,5,6,7,8,9). This variant requires both Sudoku logic and permutation reasoning.
At a Glance
| Constraint type | Outside Clues |
| Typical givens | 4–10 clue values |
| Difficulty rating | ★★★★☆ 4/5 |
| Avg. solve time — Easy | 12 min |
| Avg. solve time — Medium | 25 min |
| Avg. solve time — Hard | 50 min |
| Avg. solve time — Expert | 80 min |
How to Solve Skyscraper Sudoku
| Technique | What it does | Level |
|---|---|---|
| Clue 1 Forces 9 First | A visibility clue of 1 means the first building from that edge must be a 9. All shorter buildings behind it are hidden. | Beginner |
| Clue 9 Forces Ascending Order | A clue of 9 means all buildings are visible, so digits are in strictly ascending order from that edge: 1, 2, 3, 4, 5, 6, 7, 8, 9. | Beginner |
| Permutation Enumeration | For each clue value V, enumerate all permutations of 1–9 that give exactly V visible buildings. Cross-reference opposite-edge clues. | Intermediate |
| 9 Always Visible | The digit 9 is always visible from either edge. The digit 8 is visible only if it appears before any 9 from that edge. | Intermediate |
| Multi-Edge Constraint | Combine the clue from one edge with the opposite edge's clue. Both must be simultaneously satisfiable. | Advanced |
Average Solve Times
Easy
12 min
Medium
25 min
Hard
50 min
Expert
80 min
Frequently Asked Questions
When is a building 'visible'?
A building is visible if no taller building stands between it and the viewing edge.
Does 9 always count as visible?
Yes — 9 is always visible since it's the tallest building.
Do all rows and columns have clues?
Not necessarily — some positions outside the grid are blank, providing no constraint for that row or column.