Less taolu

https://ac.nowcoder.com/acm/contest/338/J

题解：出题人就喜欢玩你，递归会超时，需要改写成递推。

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q,ans;
ll a[N];
char str;
long long func(int x){
    if (x==1||x==0){
        return 1;
    }
    return (x*func(x-1)+(x-1)*func(x-2))%MOD;
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    a[0]=a[1]=1;
    for(int i=2;i<N;i++){
        a[i]=(i*a[i-1]+(i-1)*a[i-2])%MOD;
    }
    cin>>n;
    cout<<a[n];
    //cout << "Hello world!" << endl;
    return 0;
}