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

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

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