算法：搜索

题意：相邻的两个数之和是素数，别忘了最后一个，和第一个

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

6

8

Sample Output

Case 1:

1 4 3 2 5 6

1 6 5 2 3 4

Case 2:

1 2 3 8 5 6 7 4

1 2 5 8 3 4 7 6

1 4 7 6 5 8 3 2

1 6 7 4 3 8 5 2

代码：

#include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         using namespace std;int a[30],b[45],n,m,c[30];void cmp(){   memset(b,1,sizeof(b));    b[1]=b[0]=0;	for(int i=2;i<=22;i++)	{		for(int j=2*i;j<45;j=j+i)		    b[j]=0;	}}void dfs(int x,int k){	if(k==n&&b[c[0]+c[n-1]])	{		for(int i=0;i
         
          >n) { for(i=1;i<=n;i++) a[i]=0; c[0]=1; cout<<"Case "<<++j<<":"<