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