x x 4 x x 3 x 7 x
x 8 x x 7 x x x x
x 7 x x x 8 2 x 5

4 x x x x x 3 1 x 
9 x x x x x x x 8
x 1 5 x x x x x 4

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