Skyscraper
A single-digit pattern: a digit is a conjugate pair in two rows that share a base column, eliminating it from any cell that sees both roof cells.
When to use it
Use when a digit forms a conjugate pair (only two spots) in two rows that share one column — the base of the skyscraper.
Worked example
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Digit 7 forms a conjugate pair in two rows that share a base column; the far ends are the roof.
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Any cell that sees both roof cells cannot be 7, so the 7 is removed there.
Common mistakes
- Using lines where the digit appears three or more times — the base must be a true conjugate pair.
- Eliminating from a cell that sees only one of the two roof cells.
Frequently asked questions
What is a Skyscraper in Sudoku?
A single-digit pattern: a digit is a conjugate pair in two lines that share one base line, and the two far 'roof' cells eliminate that digit from any cell seeing both.