Apple - Hdu5160

 1 #include<cstdio>
 2 #include<algorithm>
 3 using namespace std;
 4 
 5 const long long p=1e9+7;
 6 long long a[100100],fac[100100],ans;
 7 int n,t;
 8 
 9 long long power(long long a,long long b){
10     if(a<=1)return a;
11     if(b==0)return 1;
12     if(b==1)return a;
13     long long tmp=power(a,b>>1);
14     tmp=(tmp*tmp)%p;
15     if(b&1==1)tmp=(tmp*a)%p;
16     return tmp;
17 }
18 
19 long long C(int m,int n){
20     if(m==0)return 1;
21     if(n<0)return 0;
22     long long tmp=(fac[n]*power(fac[m],p-2))%p;
23     tmp=(tmp*power(fac[n-m],p-2))%p;
24     return tmp;
25 }
26 
27 int main(){
28     scanf("%d",&t);
29     int i,j,s,k,l;
30     fac[0]=1;
31     for(i=1;i<=100000;i++)fac[i]=(fac[i-1]*i)%p;
32     for(l=1;l<=t;l++){
33         ans=0;
34         scanf("%d",&n);
35         for(i=1;i<=n;i++)scanf("%I64d",&a[i]);
36         a[n+1]=0;
37         sort(a+1,a+1+n);
38         s=k=0;
39         long long div=1;
40         for(i=1;i<=n;i++){
41             ++k;
42             if(a[i]!=a[i+1]){
43                 long long tmp,ss=0;
44                 tmp=(fac[s]*fac[k])%p;
45                 tmp=(tmp*fac[n-s-k])%p;
46                 tmp=(tmp*C(s,n))%p;
47                 for(j=1;j<=k;j++)ss+=(((a[i]*j)%p)*C(k-j,n-s-j-1))%p;
48                 ss%=p;
49                 ans+=(ss*tmp)%p;
50                 ans%=p;
51                 div=(div*fac[k])%p;
52                 s+=k;
53                 k=0;
54             }
55         }
56         ans=(ans*power(div,p-2))%p;
57         printf("Case #%d: %I64d\n",l,ans);
58     }
59     return 0;
60 }