How to solve Sudoku advanced techniques?

To solve Sudoku with advanced techniques, build accurate candidate lists and look for patterns that let you eliminate candidates without placing a digit immediately. Useful patterns include locked pairs and triples, X-Wing, XY-Wing, Swordfish, coloring, and forcing chains.

Master the prerequisite techniques first

Advanced patterns only work when the candidate marks are complete. Before searching for one, scan again for naked singles, hidden singles, pairs, and pointing candidates. A single missed basic elimination can make an advanced pattern look more complicated than it is.

Choose the pattern that matches the grid

The illustrated Sudoku tips and techniques guide shows the progression from singles through X-Wing. Practice one family at a time on hard or expert puzzles instead of trying to recognize every named technique at once.

• X-Wing: one digit appears in exactly two matching columns across two rows, or two matching rows across two columns.
• XY-Wing: three two-candidate cells link together so one shared candidate can be removed from cells that see both wings.
• Swordfish: an X-Wing expanded across three rows and three columns.
• Coloring: follow a chain of two-position candidates and alternate colors to expose a contradiction or shared elimination.
• Forcing chain: test the logical consequences of a candidate until every branch produces the same result.