uva - 524 - Prime Ring Probl（素数环、回溯）

来源：互联网发布：好听的傣族网络歌曲编辑：程序博客网时间：2024/05/22 09:06

题意：素数环。

方法：回溯，参见刘汝佳《算法入门经典》P127。

注意：有些n没有素数环，例如11。。刚开始以为程序除了问题，用了uva toolkit才知道的，数和数之间的空格，样例之间空行卡的很严，注意！

#include <iostream>#include <iomanip>#include <string>#include <cstring>#include <cstdio>#include <queue>#include <stack>#include <algorithm>#include <cmath>using namespace std;int isp[100], A[20], vis[20], n = 0;int is_prime(int n){int i = 0;for (i = 2; i <= sqrt(n); i++)if (0 == n % i)return 0;return 1;}void dfs(int cur){int i = 0, j = 0;if (cur == n && isp[A[0] + A[cur-1]]){for (i = 0; i < n; i++){if (i != n-1)cout << A[i] << " ";elsecout << A[i];}cout << endl;}else{for (i = 2; i <= n; i++){if (!vis[i] && isp[i+A[cur-1]]){vis[i] = 1;A[cur] = i;dfs(cur+1);vis[i] = 0;}}}}int main(){#ifdef Localfreopen("a.in", "r", stdin);freopen("a.out", "w", stdout);#endifint i = 0, t = 0;while(cin >> n){memset(A, 0, sizeof(A));memset(vis, 0, sizeof(vis));memset(isp, 0, sizeof(isp));if (t)cout << endl;cout << "Case " << ++t << ":" << endl;for (i = 2; i <= n*2; i++)isp[i] = is_prime(i);A[0] = 1;dfs(1);}}

1 0