HDU 1016Prime Ring Problem

http://acm.hdu.edu.cn/showproblem.php?pid=1016

题意：输入一个数，给出符合要求的素数环。

经典的dfs遍历。

#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;

int visited[25];
int pos[25];
int n, kase = 0;

int judge(int x)                 //判断是否为素数
{
    for (int i = 2; i <= sqrt(x); i++)
    {
        if (x%i == 0)     return 0;
    }
    return 1;
}

void dfs(int x,int count)
{
    pos[count] = x;
    visited[x] = 1;
    if (count == n && judge(x + pos[1]))
    {
        for (int i = 1; i < n; i++)
            cout << pos[i] << " ";
        cout << pos[n];
        cout << endl;
    }
    for (int k = 2; k <= n; k++)
    {
        if (!visited[k] && judge(k+pos[count]))
        {
            dfs(k, count+1);
            visited[k] = 0;
        }
    }
}

int main()
{
    while (cin >> n && n)
    {
        memset(visited, 0, sizeof(visited));
        memset(pos, 0, sizeof(pos));
        kase++;
        cout << "Case " << kase << ":" << endl;
        dfs(1,1);
        cout << endl;
    }
    return 0;
}