Brush up your math skills, you are going to need it for Sudoku. In classic Sudoku, the objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 subgrids that compose it contain all of the digits from 1 to 9. You will get a partially completed grid, and you need to fill in the rest. Remember, you account repeat numbers.