Sudoku is a logic-based, combinatorial number-placement puzzle. In classic Sudoku, the objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 subgrids that compose the grid contains all of the digits from 1 to 9. One of the most important strategies to solve difficult Sudoku puzzles is the “naked pair” strategy.
A naked pair occurs when two cells within a block, row, or column contain only the same two possible values. For example, if two cells in a block contain only the possible values 2 and 5, then those two cells must contain those two values, and no other cells in the block can contain those values. This means that any other cells in the block that contain either 2 or 5 can be eliminated as possibilities.
