All Sudoku Variants
9×9 · Arithmetic

Skyscraper Sudoku

Also known as Skyscrapers Sudoku, Wolkenkratzer Sudoku

Clues outside the grid count how many digits are "visible" along that row or column, reading each digit as a building height — a taller digit hides every smaller one behind it.

5 3 4 6 7 8 9 1 25

An example Skyscraper puzzle: reading row 1 from the clue, five buildings are visible (5, 6, 7, 8, 9 — taller ones hide shorter), so the clue is 5.

Skyscraper Sudoku keeps every rule of a normal 9×9 Sudoku and adds clues around the outside. Each clue treats the digits in its row or column as building heights and tells you how many buildings are visible looking in from that edge — because a taller digit hides every shorter one standing behind it.

The rule: count what you can see

Read a clue as a viewpoint. Walk along its row or column from that edge: a digit is visible only if it is taller than everything before it. The tallest digit, 9, always blocks the rest, so a clue of 1 means 9 sits right at that edge, and a clue of 9 means the digits climb 1, 2, 3, … 9 away from it.

3 1 3 2 9 4 5 6 7 8 2

One Sudoku row (blue) with its two outside clues (grey). From the left you see 1, 3 and 9 — three visible, so the left clue is 3. From the right you see 8, then 9 — two visible, so the right clue is 2.

A worked example, step by step

Step 1 — read the extremes. A clue of 1 forces a 9 against that edge; a clue of 9 forces the full ascending run 1–9. These are free placements before you touch the digits.

Step 2 — bound the near cells. A small clue like 2 means only two digits are ever visible, so after the first digit the next visible one must be the 9 — everything between them is shorter and hidden. That sharply limits which digit can sit at the edge.

Step 3 — hand back to Sudoku. Every digit a clue forces is an ordinary given for its row, column and box, so the usual Sudoku scanning takes over and cascades from there.

Solving strategy

  • Start with 1s and 9s. A clue of 1 places a 9 instantly; a clue of 9 fills the whole line 1–9. Highest value, least effort.
  • Small clues pin the edge. A clue of 2 or 3 forces the tallest digits to bunch near the far side, freeing the edge cell.
  • Clues on both ends interact. The left and right clues of the same line constrain each other — a big clue one way often forces a small one the other.
  • Feed the grid. Treat every deduced digit as a normal given and re-scan its unit for singles.

Common mistakes

  • Counting hidden digits. Only digits taller than everything before them count — a tall digit hides all shorter ones behind it.
  • Forgetting it is still Sudoku. The row, column and box no-repeat rules always apply on top of the visibility clues.
  • Misreading direction. Each clue counts from its own edge inward; the two ends of a line usually give different totals.

Can I play it here?

Not yet — Skyscraper Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile: