light oj 1095 组合数学

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <stdlib.h>
 4 #include <math.h>
 5 #include <iostream>
 6 #include <algorithm>
 7 #include <climits>
 8 #include <queue>
 9 #define ll long long
10 
11 using namespace std;
12 
13 
14 const int MAX = 200005;
15 const ll MOD = 1e9+7;
16 ll F[1010],C[1010][1010];
17 
18 void init()
19 {
20     F[0] = 1;
21     F[1] = 0;
22     F[2] = 1;
23     for(int i = 3; i <= 1000; i++)
24         F[i] = (i-1)*(F[i-1]+F[i-2])%MOD;
25 
26     for(int i = 0; i <= 1000; i++)
27     {
28         for(int j = 0; j <= i; j++)
29         {
30             if(j == 0)
31                 C[i][j] = 1;
32             else
33                 C[i][j] = (C[i-1][j]+C[i-1][j-1])%MOD;
34         }
35     }
36 }
37 
38 void solve()
39 {
40     int n,m,k;
41     scanf("%d %d %d",&n,&m,&k);
42     ll ans = 0;
43     for(int i = 0; i <= n-m; i++)
44     {
45         ans += (C[n-m][i]*F[n-k-i]);
46         ans %= MOD;
47     }
48     ans *= C[m][k];
49     ans %= MOD;
50     printf("%lld\n",ans);
51 }
52 
53 int main(void)
54 {
55     init();
56     int t,cnt = 0;
57     scanf("%d",&t);
58     while(t--)
59     {
60         printf("Case %d: ",++cnt);
61         solve();
62     }
63     return 0;
64 }