4827 妹子[快速乘法]

#include<cstdio>
#include<iostream>
using namespace std;
int n,m;
int A(int n){
    int res=1;
    for(int i=n;i>1;i--){
        res*=i;
    }
    return res;
}
int solve(int n,int m){
    return A(m-1)*A(n-1)*(2+(n-1)*(n-2));
}
int main(){
    scanf("%d%d",&n,&m);
    printf("%d\n",solve(n,m));
    return 0;
}

#include<cstdio>
#include<iostream>
using namespace std;
const int mod=100000007;
int go(int x,int y){//快速乘法 x*y
    int res=0;
    while(y){
        if(y&1) res=(res+x)%mod;
        y>>=1;
        x=(x+x)%mod;
    }
    return res%mod;
}
int A(int n){
    int res=1;
    for(int i=n;i>1;i--)
        res=go(res,i);
    return res;
}
int solve(int n,int m){
    return go(go(A(m-1),A(n-1)),(2+go((n-1),(n-2))));
}
int main(){
    int n,m;
    scanf("%d%d",&n,&m);
    printf("%d\n",solve(n,m));
    return 0;
}