Swordfish

How It Works

Swordfish extends the X-Wing pattern to three rows and three columns. When a candidate appears in at most two cells per row across three rows, and those cells collectively span exactly three columns, the candidate can be eliminated from other cells in those three columns.

Step by Step

1. Find three rows where a candidate appears in only 2-3 cells each.
2. Check if all those cells fall within exactly three columns.
3. Eliminate that candidate from other cells in those three columns.

When to Use

Use Swordfish when X-Wing doesn't apply but a similar pattern exists across three rows and three columns. A candidate appears in 2-3 cells per row across three rows, and those cells span exactly three columns.

Example

The number 4 appears in rows 1, 4, and 7. In row 1 it's in columns 2 and 5; in row 4 in columns 2 and 8; in row 7 in columns 5 and 8. The columns 2, 5, 8 form the swordfish. Eliminate 4 from other cells in those columns.

Common Mistakes

Assuming any three rows and three columns with the candidate form a swordfish. The cells must collectively span exactly three columns (or rows), and the pattern must be valid for eliminations.

Tips

Swordfish is an extension of X-Wing. If you're comfortable with X-Wing, look for the same logic with three rows/columns. Pencil marks are essential.