Skyscraper

Level 5 · Orange Belt

Strategy:

Single-Digit Patterns

Requires:

Learn after:

Two-String Kite

Overview

Skyscraper is a single-candidate pattern using two conjugate pairs. When two rows each have exactly two cells with a candidate, sharing one column but not the other, eliminations are possible from cells seeing both "roof" cells.

How It Works

Find two rows where a candidate appears in exactly two cells each.
Two of the four cells must share the same column (the "base").
The other two cells (the "roof") must be in different columns.
Eliminate the candidate from cells that see both roof cells.

Example

Look for Skyscraper.

Sudoku grid showing the initial puzzle state for Look for Skyscraper.

1

Skyscraper

Check digit 9 in rows 6 and 8.

Sudoku grid illustrating step 1: Skyscraper — Check digit 9 in rows 6 and 8.

2

Skyscraper

Each row has exactly 2 cells with candidate 9, forming conjugate pairs.

Sudoku grid illustrating step 2: Skyscraper — Each row has exactly 2 cells with candidate 9, forming conjugate pairs.

3

Skyscraper

The pairs share column 5 as a common endpoint, forming a Skyscraper pattern.

4

Skyscraper

Either r6c3 or r8c2 must contain 9, so these cells that see both cannot keep 9: r5c2 and r9c3.

Sudoku grid illustrating step 4: Skyscraper — Either r6c3 or r8c2 must contain 9, so these cells that see both cannot keep 9: r5c2 and r9c3.

5

Skyscraper

Remove 9 from the cells that see both r6c3 and r8c2: r5c2 and r9c3.

Sudoku grid illustrating step 5: Skyscraper — Remove 9 from the cells that see both r6c3 and r8c2: r5c2 and r9c3.

6

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Skyscrapers are easier to spot than X-Wings when columns don't align.
The pattern resembles two buildings with different heights.
One of the two roof cells must contain the candidate.