Skyscraper

Overview

A Skyscraper uses two conjugate pairs on the same digit that share one end in the same column (or row), forming a shape like two buildings of different heights. Candidates can be eliminated from cells that see both non-shared ends.

How It Works

Find two rows where a candidate digit appears in exactly two cells each (conjugate pairs). If one cell from each pair shares a column -- the 'base' -- the other two cells are the 'tops'. Since each pair is a strong link, at least one top must contain the digit. Therefore, any cell that sees both tops cannot contain that digit.

When To Use It

Look for Skyscrapers when you find two rows (or columns) that each contain a digit in exactly two positions. Check if one position from each pair aligns in the same column (or row).

How To Detect It

For each digit, scan rows for exactly two candidate positions. Take pairs of such rows and check if they share one column. If so, the non-shared cells are the 'tops' -- eliminate the digit from cells that see both tops.

Visual Example

A Skyscraper on one digit is hiding here. Use it to eliminate, then fill the Naked Single that results.