X-Wing Technique
advancedA powerful pattern based on two rows and two columns
X-Wing is a pattern where a candidate appears in exactly two positions in two rows, forming a rectangle.
Understanding the Concept
A candidate appears exactly twice in two different rows, and these four occurrences form a rectangle.
The same pattern can occur with columns instead of rows.
Due to Sudoku constraints, the candidate must appear in opposite corners of the rectangle.
Therefore, the candidate can be eliminated from all cells that see both positions in the columns (or rows).
Named "X-Wing" because connecting the corners forms an X pattern.
This is the simplest "fish" pattern (2x2 fish).
Examples
Row-based X-Wing
If candidate 7 appears only in R2C3, R2C7, R8C3, R8C7, then 7 can be eliminated from all other cells in columns 3 and 7.
Pro Tips
- •Look for candidates that appear exactly twice in two rows
- •Check if they form a rectangle
- •Eliminations occur in the perpendicular direction
- •X-Wings are relatively rare but very powerful
