Enter a 9x9 board with spaces for blanks.
A solution is:
1 7 6 4 9 2 5 3 8 
8 3 2 5 1 7 6 4 9 
5 9 4 8 3 6 7 1 2 
2 6 7 9 5 4 3 8 1 
4 8 1 2 6 3 9 7 5 
9 5 3 1 7 8 4 2 6 
7 1 9 3 2 5 8 6 4 
6 4 5 7 8 1 2 9 3 
3 2 8 6 4 9 1 5 7