X-Wing Technique
The X-Wing is a powerful elimination technique that helps you remove candidates when the same value appears in exactly two positions in two different rows or columns.
Advanced
What is X-Wing?
An X-Wing pattern occurs when a candidate number appears in exactly two cells in two different rows, and these cells are in the same two columns. This forms a rectangle (or X-shape) that allows you to eliminate candidates.
How to Identify an X-Wing
- Find a number that appears as a candidate in exactly two cells in a row
- Find a second row where that same number also appears in exactly two cells, in the same columns
- Eliminate this number from all other cells in those two columns
Example
Suppose the number 7 can only be in columns 2 and 8 in row 1, and also only in columns 2 and 8 in row 6. Then 7 must be either in (row1,col2) and (row6,col8), or in (row1,col8) and (row6,col2). In both cases, you can remove 7 as a candidate from all other cells in columns 2 and 8.
Pro Tips
- Start looking for X-Wing patterns with numbers that are already partially filled in
- Use pencil marks consistently to recognize X-Wing patterns