Sudoku Challenges is a logic-based, combinatorial number-placement puzzle. The objective is to fill a 9 × 9 grid with digits so that each column, each row, and each of the nine 3 × 3 sub-grids that compose the grid (also called 'boxes' or 'blocks') contain all of the digits from 1 to 9. Each puzzle will start at a partially completed grid, which has a single solution.