（深搜） — — hdu 1016

Prime Ring Problem

Problem Description

A ring is compose of n circles as shown in diagram. Put natural number 1, 2, ..., n into each circle separately, and the sum of numbers in two adjacent circles should be a prime.

Note: the number of first circle should always be 1.

 

Input

n (0 < n < 20).

 

Output

The output format is shown as sample below. Each row represents a series of circle numbers in the ring beginning from 1 clockwisely and anticlockwisely. The order of numbers must satisfy the above requirements. Print solutions in lexicographical order.

You are to write a program that completes above process.

Print a blank line after each case.

 

Sample Input

68

 

Sample Output

Case 1:1 4 3 2 5 61 6 5 2 3 4Case 2:1 2 3 8 5 6 7 41 2 5 8 3 4 7 61 4 7 6 5 8 3 21 6 7 4 3 8 5 2

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

坑啊，就多输出一个空格，一直没有AC，浪费了我好长时间的，切记切记看好输出

#include<stdio.h>#include<string.h>int p[100],a[30],n;int prim(int x){if(x<2)return 0;for(int i=2;i<x;i++)if(x%i==0)return 0;return 1; }void find(int q){if(q==n+1 && prim(a[n]+a[1])){printf("%d",a[1]);for(int i=2;i<=n;i++){printf(" %d",a[i]);}printf("\n");return ;}if(q==n+1)return ;for(int i=2;i<=n;i++){if(prim(i+a[q-1])){if(!p[i]){a[q]=i;p[i]=1;find(q+1);p[i]=0;}}}}int main(){int k=1;while(~scanf("%d",&n)){memset(p,0,sizeof(p));printf("Case %d:\n",k++);a[1]=1;if(n%2==0)find(2);printf("\n");}return 0;}