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