Sudoku is a puzzle that needs little introduction. The object is to put a digit from 1 to N in each cell of the grid so that every row, column, and bold region contains each digit once, where N is the number of rows and columns in the puzzle. (Usually N = 9.)
A Sudoku puzzle consists of 81 cells which are divided into nine columns, rows and regions. The task is now to place the numbers from 1 to 9 into the empty cells in such a way that in every row, column and 3×3 region each number appears only once. A Sudoku has at least 17 given numbers but normally there are 22 to 30.