board :: Grid
board = [['5','3','0','0','7','0','0','0','0'],
         ['6','0','0','1','9','5','0','0','0'],
         ['0','9','8','0','0','0','0','6','0'],
         ['8','0','0','0','6','0','0','0','3'],
         ['4','0','0','8','0','3','0','0','1'],
         ['7','0','0','0','2','0','0','0','6'],
         ['0','6','0','0','0','0','2','8','0'],
         ['0','0','0','4','1','9','0','0','5'],
         ['0','0','0','0','8','0','0','7','9']]
board :: Grid
board = [['5','3','0','0','7','0','0','0','0'],
         ['6','0','0','1','9','5','0','0','0'],
         ['0','9','8','0','0','0','0','6','0'],
         ['8','0','0','0','6','0','0','0','3'],
         ['4','0','0','8','0','3','0','0','1'],
         ['7','0','0','0','2','0','0','0','6'],
         ['0','6','0','0','0','0','2','8','0'],
         ['0','0','0','4','1','9','0','0','5'],
         ['0','0','0','0','8','0','0','7','9']]
board = [['5','3','0','0','7','0','0','0','0'],
         ['6','0','0','1','9','5','0','0','0'],
         ['0','9','8','0','0','0','0','6','0'],
         ['8','0','0','0','6','0','0','0','3'],
         ['4','0','0','8','0','3','0','0','1'],
         ['7','0','0','0','2','0','0','0','6'],
         ['0','6','0','0','0','0','2','8','0'],
         ['0','0','0','4','1','9','0','0','5'],
         ['0','0','0','0','8','0','0','7','9']]