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

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

x x x  x 4 9  1 x 8
4 5 x  x x 8  x x x
x x 9  6 x x  x x x