Back to Sudoku Rules
🧠 Sudoku Rules

📋 Swordfish – Advanced Technique

Three rows/columns share exactly three columns/rows for a digit. Eliminate that digit from all other cells in those lines. Illustrated guide.

What Is Swordfish?

Swordfish generalizes the X-Wing. For a digit (here 1), three rows are restricted to the same three columns (or vice versa: three columns restricted to the same three rows). Then that digit can be eliminated from all other cells in those columns/rows.

Step-by-Step Example

Step 1: Scan candidates for 1 — three rows share the same three columns
1) Candidate scan shows three rows where 1s occur only within three specific columns.
Step 2: Confirm the 3×3 pattern (three rows × three columns)
2) Pattern confirmed ⇒ Swordfish.
Step 3: Eliminations and resulting placements
3) Remove 1 from the remaining cells of those columns; follow-up singles appear.

Where It Works

  • Row-based swordfish: 3 rows → same 3 columns,
  • Column-based swordfish: 3 columns → same 3 rows.

Common Pitfalls

  • Allowing more than three columns/rows — the pattern must be exactly 3×3.
  • Confusing it with X-Wing (which uses only two lines).
More Sudoku RulesAll RulesPlay Sudoku