Author: loop3r
Date: 20260314
tag: 递推
link: https://www.luogu.com.cn/problem/P1595

问题描述

link

分析

略

参考代码

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

int n;
long long f[25];

int main() {
	cin >> n;

	f[1] = 0;
	f[2] = 1;
	for (int i = 3; i <= n; i++) {
		f[i] = (i - 1) * (f[i - 1] + f[i - 2]);
	}
	cout << f[n] << endl;

	return 0;
}