UESTC 电子科大专题训练 数论 E

UESTC 1716

题意：中文题

思路：先把男生排列，由于是圆桌，所以每个位置都是一样的，排列方案为A(n,n)/n，再对女生排列，由于男生已经在座位上了，所以此时每个座位是不一样的，方案数为A(n,n)

AC代码：

#include "iostream"
#include "string.h"
#include "stack"
#include "queue"
#include "string"
#include "vector"
#include "set"
#include "map"
#include "algorithm"
#include "stdio.h"
#include "math.h"
#define ll long long
#define bug(x) cout<<x<<" "<<"UUUUU"<<endl;
#define mem(a) memset(a,0,sizeof(a))
#define mp(x,y) make_pair(x,y)
#define pb(x) push_back(x)
using namespace std;
const long long INF = 1e18+1LL;
const int inf = 1e9+1e8;
const int N=1e5+100;
const ll mod=1e9+7;

ll ans=1;
int main(){
    ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
    int n;
    cin>>n;
    for(int i=2; i<n; ++i){
        ans*=i*i;
    }
    cout<<ans*n<<"\n";
    return 0;
}