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Sudoku is a logic-based number puzzle. Fill a 9×9 grid so every row, column, and 3×3 box contains digits 1–9 exactly once. A valid puzzle has exactly one solution. Sudoku requires no arithmetic — just logical deduction.

Trin-for-trin guide

1. 1Naked singles: a cell can only contain one digit
2. 2Hidden singles: a digit can only go in one cell within a row/column/box
3. 3Naked pairs/triples: eliminate candidates from other cells
4. 4Advanced: X-wings, swordfish, and coloring techniques

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