牛客OI赛制测试赛 F：子序列

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题目传送门
代码：

#include<bits/stdc++.h>
using namespace std;

typedef long long LL;
const int maxn=1000+100;
const LL mod=1e9+7;
const LL M=mod-1;

int ans[maxn];
LL fac[maxn][maxn];

LL mypow(LL a,LL b){

    LL sum=1;
    while(b){

        if(b&1) sum=sum*a%mod;
        a=a*a%mod;
        b>>=1;
    }
    return sum;
}

int main(){

    int T;
    scanf("%d",&T);
    for(int i=0;i<maxn;i++){

        fac[i][0]=1;
        for(int j=1;j<=i;j++) fac[i][j]=fac[i-1][j-1]+fac[i-1][j],fac[i][j]%=M;
    }
    while(T--){

        int n,k;
        scanf("%d%d",&n,&k);
        for(int i=1;i<=n;i++) scanf("%d",&ans[i]);
        sort(ans+1,ans+1+n);
        LL sum=1;
        for(int i=2;i<n;i++){

            sum=sum*mypow(ans[i],((fac[n-1][k-1]-fac[i-1][k-1]-fac[n-i][k-1])%M+M)%M)%mod;
        }
        printf("%lld\n",sum);
    }
}