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