CodeVS 1031 质数环(DP）

题目大意：

http://codevs.cn/problem/1031/

#include <iostream>
#include <cmath>
#include <algorithm>
#include <string>

using namespace std;

int arr[17] = {0};
bool f[17] = {false};

bool isPrime(int a)
{
    if(a == 0)
        return false;
    if(a == 1)
        return true;

    for(int i = 2; i <= sqrt(a); i++)
    {
        if(a % i == 0)
            return false;
    }

    return true;
}

void dfs(int a, int n)
{
    if(a == n && isPrime(arr[n-1] + arr[0]))
    {
        for(int i = 0; i < n; i++)
            cout << arr[i] << " ";
        cout << endl;
        return;
    }

    for(int i = 2; i <= n; i++)
    {
        if(!f[i] && isPrime(i + arr[a-1]))
        {
            arr[a] = i;
            f[i] = true;
            dfs(a+1,n);
            f[i] = false;

        }
    }
}

int main()
{
    int n;
    cin >> n;
    arr[0] = 1;
    f[0] = true;
    dfs(1,n);
    return 0;
}