- Time limit: 1.00 s
- Memory limit: 512 MB
Input
The first input line has an integer $n$: the size of the grid.
After this, there are $n$ lines that describe the grid. Each line has $n$ characters:
.
means an empty square, and A
and B
show the characters already placed.You can assume that every row and column has at most one A and B.
Output
Print one integer: the number of ways modulo $10^9+7$.
Constraints
- $2 \le n \le 500$
Input:
5
.....
..AB.
.....
B....
...A.
Output:
16