> 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!
> 
> 

• i guess maybe this problem is np-something... (0) frkstyc 2008-02-13 22:47:59
  • Maybe. But if it is, how to prove it? I mean, how to make the reduction? (0) chipmunk 2008-02-14 10:08:57
• up (0) chipmunk 2008-02-17 02:27:53