Skyscraper Sudoku
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How to play Skyscraper Sudoku
Standard Sudoku rules apply. Each blue clue number tells you how many digits are visible looking into the grid from that edge — a digit is visible only if it is larger than all digits before it from that direction.
Full guide →
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
What is Skyscraper Sudoku?
Skyscraper Sudoku is a variant where numbers appear outside the grid on all four sides. Each number tells you how many distinct 'buildings' (digits) are visible when looking into that row or column from that side. Taller buildings hide shorter ones behind them — a larger digit blocks any smaller digit placed further into the row.
How does visibility work in Skyscraper Sudoku?
Imagine the digits in a row as buildings of different heights. Looking from one end, you can see a building only if no taller building stands between you and it. A clue of 1 means only the first building is visible, so it must be the tallest (digit 9). A clue of 9 means all buildings are visible, so the row must be in ascending order from that side.
What do extreme clue values tell me?
A clue of 1 means the first cell from that side holds a 9 — it blocks everything else. A clue of 9 means the row or column is in strictly ascending order from that direction (1,2,3,4,5,6,7,8,9). Both are immediately actionable. Mid-range clues require enumerating valid permutations.
Is Skyscraper Sudoku harder than regular Sudoku?
Yes, generally. Skyscraper clues require enumerating valid digit permutations for each row and column, which is more combinatorially intensive than classic Sudoku elimination. Easy puzzles are accessible; hard and expert puzzles require tracking visibility across multiple rows and columns simultaneously.
What is the best first strategy for Skyscraper Sudoku?
Start with clues of 1 and 9 — they immediately fix a digit or fully determine the order of a row. Then look for clues of 2, which constrain the position of the 9 significantly. Combine skyscraper deductions with standard Sudoku box and row/column scans.
How long does Skyscraper Sudoku take to solve?
Easy puzzles take 8–20 minutes. Medium puzzles run 20–40 minutes. Hard puzzles average 40–75 minutes and expert puzzles often exceed 90 minutes. Fast solvers develop the ability to enumerate valid visibility permutations quickly without writing them all out.