- Time limit: 1.00 s
- Memory limit: 512 MB
Your task is to count the number of ways k bishops can be placed on an n \times n chessboard so that no two bishops attack each other.
Two bishops attack each other if they are on the same diagonal.
The only input line has two integers n and k: the board size and the number of bishops.
Print one integer: the number of ways modulo 10^9+7.
- 1 \le n \le 500
- 1 \le k \le n^2