Sudoku is a logic-based, combinatorial number-placement puzzle.
The objective is to fill a 9 x 9 grid with digits so that each
column, each row, and each of the 3 x 3 sub-grids that compose
the grid (also called "boxes", "blocks", "regions" or "sub-squares")
contain all of the digits from 1 to 9. The game provides a partially
completed grid, which has a unique solution.
Completed puzzles are always a type of Latin square with an additional
constraint on the contents of individual regions. For example, the
same single integer may not appear twice in the same 9x9 playing board
row or column or in any of the nine 3x3 sub-regions of the 9x9 playing
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