X-Wing: Step-by-Step Guide
An X-Wing occurs when a digit appears as candidates in exactly two cells in two different rows (same columns) or two different columns (same rows), forming a rectangle. Those columns/rows elsewhere cannot contain the digit.
Prerequisites
How to recognize it
- Pick a digit (e.g., 5). Find two rows where that digit appears in exactly two columns—and the columns match across the rows.
- The four cells form the corners of a rectangle: that’s the X-Wing.
Why it works
If a digit must occupy one of two positions in each of two rows (same columns), then those columns cannot contain the digit in any other row, enabling candidate eliminations at scale.
Try it now
Interactive example coming soon: a mini-board that highlights the rectangle and removes candidates when you confirm.
Common pitfalls
- Near misses where one row has three candidates—strictly two per row/column are required.
- Forgetting to eliminate along the orthogonal dimension (columns if you found rows, and vice versa).
Related: More advanced patterns coming soon.