Advanced Sudoku Strategies: X-Wing and Swordfish

Once basic scanning stops working on hard and expert puzzles, it's time to add pattern-based techniques to your toolkit. Two of the most powerful are the X-Wing and the Swordfish.

The X-Wing

An X-Wing forms when a candidate appears in exactly two cells in two different rows, and those cells share the same two columns. That candidate can then be eliminated from the rest of those columns.

The Swordfish

The Swordfish is the X-Wing's bigger sibling, extending the pattern across three rows and three columns. It's rarer but devastatingly effective on expert-level grids.