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