承接上一篇

升级版，别怕，上一篇弄会了，这个就是 豆芽菜✌️
https://www.acwing.com/problem/content/description/5295/

f1.递归

#include <bits/stdc++.h>  
//  2024-03-08  Come on !
using namespace std;  
#define  ll long long  
ll N;
int  solve(int n){if(n==1||n==0)  return 1;else if(n==2)  return 2;else return solve(n-3)+solve(n-2)+solve(n-1);//cout << "Hello world !" << '\n';}	
int main() {  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0); // no endll;  int t=1;while(t--){cin>>N;cout<< solve(N);}return 0;  
}

f2.记忆化

#include <bits/stdc++.h>  
//  2024-03-08  Come on !
using namespace std;  
#define  ll long long  
ll N,sum;
ll pre_res[100001];
int  solve(int n){if(n==1||n==0)  return 1;else if(n==2)  return 2;else if(pre_res[n]!=0){return pre_res[n];}else  {sum=solve(n-3)+solve(n-2)+solve(n-1);}  pre_res[n]=sum;return sum;//cout << "Hello world !" << '\n';}	
int main() {  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0); // no endll;  int t=1;while(t--){cin>>N;cout<< solve(N);}return 0;  
}

分析过程