牛客OI赛制测试赛 F：子序列

​​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);
  }
}