> In fact, it means that two 'X' -- named A and B -- can be put in different '#'s if and only if both the positions (row_A,column_B) and 
> (row_B,column_A) is not '#' -- instead of 'X'.
> 
> Sorry for described it incorrectly. I made a false analogue of 8 queens problem. It is quite different from 8 queens problem.
> 
> 
> Does anyone knows the solutions?
> Many Thanks!
> 
>