2 x x  6 7 x  x x x
x x 6  x x x  2 x 1
4 x x  x x x  8 x x

5 x x  x x 9  3 x x 
x 3 x  x x x  x 5 x
x x 2  8 x x  x x 7

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