Swordfish
Swordfish extends X-Wing to a 3-row × 3-column pattern. When a specific number’s candidates in three rows exist within only the same three columns, you can eliminate that number from other cells in those three columns.
Overview of Swordfish
Swordfish is a pattern where a number’s candidates in three rows each appear in at most three columns, and those columns total only three distinct columns. While X-Wing is a 2×2 pattern, Swordfish is a 3×3 pattern. Each row’s candidates can be in 2 or 3 columns — as long as the total stays within 3 columns, the pattern holds.
How to Use Swordfish
Focus on a specific number and check which cells in each row have it as a candidate.
Find three rows where the number appears in 2–3 columns.
If the columns used across all three rows total only 3, you have a Swordfish.
Eliminate the target number from other rows’ cells in those three columns.
Example
Suppose ‘6’ appears in columns 2 and 5 of row 1, columns 2 and 9 of row 4, and columns 5 and 9 of row 7. The columns used are 2, 5, and 9 — just three. Since ‘6’ must go somewhere in these 3 rows × 3 columns, you can remove ‘6’ from columns 2, 5, and 9 in all other rows.
Tips for Finding Swordfish
First, make sure you understand X-Wing well, then extend the concept to 3 rows × 3 columns. Find three rows where the target number has candidates in only 2–3 cells, then check if the columns total 3 or fewer. While rare, it’s essential for solving the hardest puzzles.