Sudoku solving technique · Intermediate
X-Wing
A digit locked to the same two columns in two rows leaves the rest of those columns.
What is an X-Wing?
When a candidate appears in exactly two cells in each of two different rows, and those cells share the same two columns, the candidate must go in one of the two diagonal pairs. You can eliminate it from all other cells in those two columns.
How to spot an X-Wing
Pick a digit and look for rows where it fits in exactly two cells. If two such rows have those cells in the same two columns, the four cells form the corners of a rectangle. The digit sits on one of the two diagonals, so you can remove it from every other cell in those two columns. With the roles swapped, it works the same way across two columns.
- Difficulty
- In Sudoku Pro, this technique belongs to the Intermediate level.
- Learning path
- Technique 9 of 20 on the learning path
An example from the app
| Pattern (purple). Candidates 1, 3 | Given 4 | Given 2 | Pattern (purple). Candidates 1, 3 |
| Affected cell (orange). Candidates 1, 2. Eliminated 3 | Empty | Empty | Affected cell (orange). Candidates 1, 4. Eliminated 3 |
| Pattern (purple). Candidates 3, 4 | Given 2 | Given 1 | Pattern (purple). Candidates 3, 4 |
| Affected cell (orange). Candidates 1, 4. Eliminated 3 | Empty | Empty | Given 2 |
Small digits are candidates. Crossed-out digits can be removed in this step.
- Pattern (purple)
- Affected cell (orange)