URAL——DFS找规律——Nudnik Photographer

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int vis[60];
int n;
int ans;
void dfs(int m,int num)
{
    if(num == n){
        ans++;
        return ;
    }
    for(int i = m - 2; i <= m + 2; i++){
        if(i <= 1 || i > n )
            continue;
        if(!vis[i]){
            vis[i] = 1;
            dfs(i,num+1);
            vis[i] = 0;
        }
    }
}
int main()
{
    while(~scanf("%d",&n)){
        ans = 0;
        memset(vis,0,sizeof(vis));
        vis[1] = 1;
        dfs(1,1);
        printf("%d\n",ans);
    }
    return 0;
}

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int dp[60];
int main()
{
    int n;
    dp[1] = 1;
    dp[2] = 1;
    dp[3] = 2;
    while(~scanf("%d",&n)){
        for(int i = 3; i <= n ;i++)
            dp[i] = dp[i-1] + dp[i-3] + 1;
       printf("%d\n",dp[n]);
    }
    return 0;
}