Advanced Strategies for Zen Masters | 20 Minute Read
An X-Wing pattern occurs when a candidate appears exactly twice in two different rows, and those occurrences share the same two columns. This allows you to eliminate that candidate from all other cells in those specific columns. It is a powerful 'rectangle' of logic.
The Swordfish is the triple-row expansion of the X-Wing. By identifying three rows where a candidate is limited to the same three columns, you can clear that number from those columns across the entire 9x9 grid. These techniques are mandatory for 'Expert' and 'Master' difficulties in Sudoku Zen.