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