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X-Wing

Advanced

A pattern of four cells forming a rectangle that eliminates candidates.

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Example diagram — highlighted cells show where the technique applies.

How It Works

X-Wing is an advanced technique. When a candidate appears in exactly two cells in each of two different rows, and those cells are in the same two columns, the candidate can be eliminated from all other cells in those two columns (and vice versa for columns/rows).

Step by Step

  1. Find a candidate that appears in exactly two cells in two different rows.
  2. Check if those four cells form a rectangle (same two columns).
  3. Eliminate that candidate from all other cells in those two columns.

When to Use

Use X-Wing when a candidate appears in exactly two cells in each of two rows (or two columns), and those four cells form a rectangle. You can eliminate that candidate from other cells in those two columns (or rows).

Example

The number 6 appears in cells (2,3) and (2,7) in row 2, and in (8,3) and (8,7) in row 8. The four cells form a rectangle. So 6 must be in column 3 or column 7. Remove 6 from all other cells in columns 3 and 7.

Common Mistakes

Not ensuring the four cells form a perfect rectangle. The two cells in each row must be in the same two columns. Also, the candidate must appear in exactly two cells per row (or column).

Tips

X-Wing is easier to spot when you've reduced candidates with pencil marks. Look for a number that appears in only two cells in each of two rows; check if they align in columns.

Practice This Technique

Try solving a puzzle and look for opportunities to apply X-Wing.

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