求满足 $\sum_{i=1}^{n} \max(p_i, q_i) = k$ 的长度为 $n$ 的排列对 $(p, q)$ 的数量。
由于答案可能很大，请输出其对 $10^9 + 7$ 取模的结果。
输入格式
仅一行，包含两个整数 $n$ 和 $k$ ($1 \le n \le 100, 1 \le k \le n^2$)。
输出格式
输出答案对 $10^9 + 7$ 取模的结果。
样例
样例输入 1
2 4
样例输出 1
2
样例输入 2
3 7
样例输出 2
12
QOJ.ac
QOJ
Limite de temps : 2 s
Limite de mémoire : 256 MB
Points totaux : 100
#2573. 两个排列
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