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