Expert sudoku
Expert puzzles need the advanced patterns: an X-Wing, an XY-Wing or a Swordfish. They are still logical from start to finish. No guessing required.
Expert0:00
Expect to spend twenty minutes or more. Keep your candidates tidy, because the patterns you need are easy to miss in a messy grid.
An X-Wing looks across two rows at once. If a number can only go in the same two columns in both rows, it cannot go anywhere else in those columns.
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