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