x 9 x  x x 4  x x 7
x x x  x x 7  9 x x
8 x x  x x x  x x x 

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

x x x  x x x  x x 4
x x 3  5 x x  x x x
2 x x  6 x x  x 8 x