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

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

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