1265: prime circle

http://tjuacm.chaosheng.top/problem.php?id=1265
https://vjudge.net/problem/HDU-1016

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>

using namespace std;

const int N = 30;

int n;
int path[N];
bool visit[N];

bool isPrime(int x){
    for(int i = 2; i * i <= x; i++){
        if(x % i == 0) return false;
    }
    return true;
}

void dfs(int pos){
    if(pos == n && isPrime(path[n-1] + 1)){
        for(int i = 0; i < n-1; i++){
            printf("%d ", path[i]);
        }
        printf("%d\n", path[n-1]);
    }
    if(pos == n) return ; 
    for(int i = 2; i <= n; i++){
        if(!visit[i] && isPrime(path[pos-1] + i)){
            path[pos] = i;
            visit[i] = 1;
            dfs(pos + 1);
            visit[i] = 0;
        }
    }
} 

int main(){
    int t = 0;
    while(cin >> n){
        t++;
        memset(visit, 0, sizeof(visit));
        path[0] = 1;
        visit[1] = 1;
        printf("Case %d:\n", t);
        dfs(1);
        printf("\n");    
    }
    return 0;
}