Sudoku (also known as Number Place) is a placement puzzle. The puzzle is most frequently a 9 x 9 grid made up of 3 x 3 subgrids (called regions). Some cells already contain numbers, known as givens. The goal is to fill in the empty cells, one number in each, so that each column, row, and region contains the numbers 1 through 9 exactly once. Each number in the solution therefore occurs only once in each of three directions, hence the single numbers implied by the puzzle's name.
