hdu 1016 Prime Ring Problem

import java.io.*;import java.util.*;public class Main{static boolean [] hash = new boolean [45];static boolean [] flag = new boolean [23];static int [] num = new int[23];static PrintWriter cout = new PrintWriter(new OutputStreamWriter(System.out));public static void main(String[] args){Scanner cin = new Scanner(System.in);Arrays.fill(hash, (boolean)false);for(int i = 2; i < 20; i++)for(int j = i + i; j < 41; j += i)hash[j] = true;int t = 1;while(cin.hasNext()){int n;Arrays.fill (flag, (boolean)false); n = cin.nextInt(); num[1] = 1; //System.out.println("Case " + t++ + ":"); cout.print("Case " + t++ + ":/r/n"); DFS(n, 1); //System.out.println(); cout.println();cout.flush();}}static void DFS(int n, int count){if(count == n ){if(!hash[ num[count] + num[1]])for(int j = 1; j <= n; j++){if(j != n)cout.print(num[j] + " ");//System.out.print(num[j] + " ");elsecout.print(num[j] + "/r/n");//System.out.println(num[j]);}}for(int i = 2; i <= n; i++){if(!hash[num[count] + i] && !flag[i]){flag[i] = true;num[count + 1] = i;DFS(n, count + 1);flag[i] = false;}}}}