Sudoku solving technique · Pro
Swordfish
The X-Wing across three rows and three columns.
What is a Swordfish?
An extension of X-Wing to three rows. When a candidate appears in only two or three cells in each of three rows, and all those cells fall within three columns, you can eliminate that candidate from all other cells in those three columns.
How to spot a Swordfish
Look for three rows where a digit fits in only two or three cells, and check whether all of those cells lie in just three columns. They do not have to fill a full grid of nine cells; it is enough that no fourth column appears. Then the digit leaves those three columns in every other row. Across three columns, it works the same way.
- Difficulty
- In Sudoku Pro, this technique belongs to the Pro level.
- Learning path
- Technique 11 of 20 on the learning path
An example from the app
| Pattern (purple). Candidates 1, 2 | Pattern (purple). Candidates 2, 3 | Empty | Given 4 |
| Empty | Pattern (purple). Candidates 2, 4 | Pattern (purple). Candidates 1, 2 | Given 3 |
| Pattern (purple). Candidates 2, 3 | Empty | Pattern (purple). Candidates 2, 4 | Given 1 |
| Affected cell (orange). Candidates 4. Eliminated 2 | Affected cell (orange). Candidates 1. Eliminated 2 | Given 3 | Empty |
Small digits are candidates. Crossed-out digits can be removed in this step.
- Pattern (purple)
- Affected cell (orange)