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