HD 1016 Prime Ring Problem(素数环问题)

题目来源 :HD 1016

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
题意就是输入一个数n,在 1 到 n 里面找数字围成一个圈,使得相邻的两个数字加起来是素数,每个环都有1,输出的结果按字典序输出,每个答案都从1 开始。

这里有一个值得注意的地方就是,最后一个数跟1的和要是素数。每个case之后都要有空行。

很显然,要用for循环进行深搜。

#include 
#include 
#include 
#include 
using namespace std;

int num[20],ans[20],bj[20];
int n,len;
void get(){    //这里是得到素数,如果一个个判断素数,会做很多重复的工作
	len=0;
	int leap,i,j;
	for(j=2;j<25;j++){
		leap=0;
		int ma=sqrt(j)+1;
		for(i=2;i



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