OJ-Problems-Source/HDOJ/5160_autoAC.cpp
2016-09-10 11:37:56 +08:00

93 lines
2.0 KiB
C++

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<cstring>
using namespace std;
#define LL __int64
const int N=100005;
const int MOD=1000000007;
LL Ext_gcd(LL a,LL b,LL &x,LL &y){
if(b==0) { x=1, y=0; return a; }
LL ret= Ext_gcd(b,a%b,y,x);
y-= a/b*x;
return ret;
}
LL Inv(LL a,int m){
LL d,x,y,t= (LL)m;
d= Ext_gcd(a,t,x,y);
if(d==1) return (x%t+t)%t;
return -1;
}
LL Cm(LL n, LL m, LL p){
LL a=1, b=1;
if(m>n) return 0;
while(m){
a=(a*n)%p;
b=(b*m)%p;
m--;
n--;
}
return (LL)a*Inv(b,p)%p;
}
struct Dt{
LL x;
int cnt;
Dt(){}
Dt(LL _x,int _c){
x=_x;
cnt=_c;
}
};
LL a[N],fro[N],bac[N];
int main(){
int T;
int n,cas=0;
scanf("%d",&T);
while(T--){
memset(fro,0,sizeof(fro));
memset(bac,0,sizeof(bac));
scanf("%d",&n);
for(int i=0;i<n;++i)
scanf("%I64d",&a[i]);
sort(a,a+n);
int len=n,cnt=1;
fro[0]=1;
for(int i=1;i<n;++i){
if(a[i]==a[i-1]){
++cnt;
fro[i]=fro[i-1];
}
else{
fro[i]=fro[i-1]*Cm(len,cnt,MOD)%MOD;
len-=cnt;
cnt=1;
}
}
LL pre=1,cnm=1;
len=cnt=1;
bac[n-1]=1;
for(int i=n-2;i>=0;--i){
++len;
if(a[i]==a[i+1]){
++cnt;
cnm=cnm*len%MOD*Inv(cnt,MOD)%MOD;
bac[i]=pre*cnm%MOD;
}
else{
cnt=1;
cnm=len;
pre=bac[i+1];
bac[i]=pre*cnm%MOD;
}
}
bac[n]=1;
LL ans=0;
for(int i=0;i<n;++i){
ans=(ans+(fro[i]*bac[i+1]%MOD*a[i]%MOD))%MOD;
}
printf("Case #%d: %I64d\n",++cas,ans);
}
return 0;
}