HDU 1016 DFS

/*

终究是自己弱爆了~~~

简单的DFS  写了那么久;

*/


/*
 *Author   ID:fuqiang11 
 *Problem  ID:HDU 1016
 *Submit Time:2013/7/22
 *Algorithm  :DFS
*/
#include <iostream>
#include <cstdio>
#include <string>
#include <cmath>
#include <cstring>
using namespace std;
#define maxn 20
bool visit[maxn];
int pre[maxn];
int n;

bool is_primer(int a) //判断素数
{
    for(int i = 2; i <= sqrt(a); i++)
        if(a%i == 0)
            return false;
    return true;
}
void prin_pre(int x)  //打印路径
{
    if(x == 1)
        printf("1");
    else
    {
        prin_pre(pre[x]);
        printf(" %d",x);
    }
}
void DFS(int st, int len)
{
    if(len == n) //达到n个
    {
        if(is_primer(st + 1)) //能构成环
        {
            prin_pre(st);
            printf("\n");
        }
    }
    else
    {
        for(int i = 1; i <= n; i++)
        {
            if(!visit[i] && is_primer(st + i))
            {
                //cout<< st <<" + "<< i <<endl;
                visit[i] = true; //访问
                pre[i] = st;  //前驱
                DFS(i,len+1);
                visit[i] = false; //回溯
            }
        }
    }
    return ;
}

int main()
{
    int Case = 1;
    while(scanf("%d",&n)!=EOF)
    {
        memset(visit,false,sizeof(visit));
        visit[1] = true;
        pre[1] = 1;
        printf("Case %d:\n",Case++);
        DFS(1,1);
        printf("\n");
    }
    return 0;
}


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