What it is
An X-Wing forms when a digit has exactly two candidate cells in each of two different rows, and those cells share the same two columns. The four cells form a rectangle: the digit must occupy one diagonal, so it can be eliminated from all other cells of both columns. The same logic works with columns and rows swapped.
How to spot it
Track one digit across the grid. List rows where it has exactly two candidate cells; when two of those rows use the same pair of columns, you have the rectangle.
Interactive example
Use Next to walk through the deduction on the board.
Step by step
- This is a candidate map for the digit 9. In the second row, 9 can only go in two cells.
- The seventh row also allows 9 in only two cells — the same two columns. The four cells form a rectangle: an X-Wing.
- Whichever diagonal of the rectangle takes the 9s, both columns are consumed. Remove 9 from every other cell in those columns.
Common mistake: Using rows that have more than two candidate cells for the digit. The pattern requires exactly two per row — otherwise the diagonal argument breaks down.
Put it into practice
Examples on this page are validated with the Play Sudoku Daily puzzle engine.