Gym Gym 101147G 第二类斯特林数

 1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 const int maxn = 1010;
 6 const long long MOD = 1000000000 + 7L;
 7 long long stir[maxn][maxn];
 8 long long fac[maxn];
 9 
10 void init() {
11 
12     fac[1] = fac[0] = 1;
13     for(int i=2;i<=1000;i++) {
14         fac[i] = fac[i-1]*i%MOD;
15     }
16 
17 
18     stir[1][1]=1;
19     for(int i=2; i<=1000; i++)
20         for(int j=1; j<=i; j++)
21             stir[i][j]=(stir[i-1][j-1]+(long long)j*stir[i-1][j]%MOD)%MOD;
22 }
23 
24 int main() {
25     freopen("galactic.in","r",stdin);
26     init();
27     int t;
28     scanf("%d",&t);
29     while(t--) {
30         int n,k;
31         scanf("%d%d",&n,&k);
32 
33         if(n>=k) {
34             printf("%I64d\n",stir[n][k]*fac[k]%MOD);
35         }
36         else puts("0");
37 
38     }
39     return 0;
40 }