Swordfish
The Swordfish is an expert-level technique that is essentially an expanded version of the X-Wing pattern. While an X-Wing uses two rows and two columns, a Swordfish uses three.
How it Works
A Swordfish pattern exists when you find a specific candidate number that is restricted to two or three cells in exactly three different rows. Crucially, those candidate cells must all align perfectly into exactly three columns.
Because the number must be placed exactly three times across those three rows, and can only fall into those three specific columns, the three resulting placements will completely "fill" the requirements for those columns.
Therefore, you can confidently eliminate that candidate number from any other cell in those three columns!
How to spot and apply Swordfish in Sudoku
- Find the patternLocate a single candidate number that is restricted to two or three columns across exactly three different rows.
- Eliminate candidatesYou can safely remove that candidate number from all other cells in those three columns.