"SUDOKU" - is a logic-based, combinatorial number-placement puzzle. The objective is to fill a 99 grid with digits so that each column, each row, and each of the nine 33 subgrids that compose the grid (also called "boxes", "blocks", or "regions") contains all of the digits from 1 to 9. The puzzle setter provides a partially completed grid, which for a well-posed puzzle has a single solution.