X-Wing sudoku technique

Find a digit that appears as a candidate in exactly two cells of one row, and exactly two cells of another row — with both pairs standing in the same two columns. The four cells draw a rectangle, and the digit must land on one of its diagonals. Either way, both marked columns receive the digit inside the rectangle, so every other candidate for it in those two columns is gone.

How to find a x-wing

1. Pick a digit and map its candidates row by row.
2. Find two rows that each hold the digit in exactly two cells, aligned on the same two columns.
3. Eliminate the digit from those two columns everywhere outside the four corner cells.
4. The same logic runs sideways: two columns aligned on two rows clear the rows instead.

The pattern on the grid

Worked example

Map digit 1 across the grid below and the four pattern cells r6c7, r6c9, r9c7, r9c9 emerge: each defining line holds the digit only inside the shared cover lines. Wherever the 1s finally land within the pattern, the cover lines are used up — which erases r2c7<>1, r2c9<>1, r7c7<>1, r7c9<>1, r8c7<>1, r8c9<>1.

When it fails

If a defining row holds the candidate in a third cell, the pattern collapses — that is not an X-Wing but a candidate for a finned variant, which has stricter elimination rules. Count twice, erase once.

Puzzles that need it

These grids come from rated games on this site — our solver confirmed that x-wing was part of the shortest solving path for each one.

Every string is the standard 81-character format (0 = empty) — paste it into any solver to verify the rating and the solving path yourself. Want to try one under the clock? Play a free puzzle — no account needed — or create an account to train specific difficulty tiers.

Related techniques

• Swordfish
• XY-Wing
• Unique Rectangle

All solving techniques