The game starts with a 9 × 9 grid, some of which squares are filled in with numbers. The player must fill the missing digits with logic and complete the grid. One should remember that
Any row should not contain more than one of the same numbers from 1-9.
Any column should not contain more than the same numbers from 1-9.
Any 3 × 3 grid should not contain more than the same numbers from 1-9.