x 4 x x x x x 9 x
x 9 7 1 x 8 2 3 x
8 x 2 x x x 5 x 7
x x x 3 8 4 x x x
x x x x 5 x x x x
x x x 6 1 2 x x x
6 x 4 x x x 3 x 9
x 1 3 4 x 5 6 8 x
x 2 x x x x x 4 x