prime ring problem（hdu 1016）

Prime Ring Problem

Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 36885 Accepted Submission(s): 16252

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
#include <stdio.h>  #include <string.h>    int hash[30];  int arr[100];  int n;    int juge(int num)  {      int i;      for(i=2;i<num;i++)          if(num%i==0)              return 0;      return 1;  }    void DFS(int order,int index)  {     int i;       arr[order]=index;   hash[index]=1;          if(order==n)        {      if(juge(arr[order]+arr[1]))       {          printf("1");         for(i=2;i<=n;i++)          printf(" %d",arr[i]);         printf("\n");       }        return ;     }     for(i=1;i<=n;i++)     {         if(!hash[i]&&juge(arr[order]+i))         {             DFS(order+1,i);             hash[i]=0;        }     }    return ;  }    int main()  {      int flag=1;      while(~scanf("%d",&n))      {        printf("Case %d:\n",flag++);        DFS(1,1);        printf("\n");      }      return 0;  }