uva 524 Prime Ring Problem

题目：Prime Ring Problem

题意：求长度为n的素数环。

思路：dfs，枚举每一位上的值。

代码：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;

bool Prime[33]={0,1,1,1,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,0,0,0,0,1,0,1,0};
int n;
vector<int> vec;
int use[33]={0};

void dfs(int x){
if(x==n){
if(!Prime[vec[vec.size()-1]+1]) return ;
printf("1");
for(int i=1;i<vec.size();i++){
printf(" %d",vec[i]);
}
printf("\n");
return ;
}
for(int i=2;i<=n;i++){
if(!use[i]&&Prime[vec[x-1]+i]){
use[i]=true;
vec.push_back(i);
dfs(x+1);
use[i]=false;
vec.pop_back();
}
}
}

int main() {
int T=0;
while(scanf("%d",&n)==1) {
if(T!=0) printf("\n");
vec.clear();
vec.push_back(1);
printf("Case %d:\n",++T);
dfs(1);
}
return 0;
}