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HDU 1016-Prime Ring Problem（DFS）

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HDU 1016-Prime Ring Problem（DFS）

Prime Ring Problem

Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 27595 Accepted Submission(s): 12271

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要求按字典序輸出素數環。。DFS爆搜，不用剪枝。。一開始用 next_permutation()函數純暴力判結果TLE了。。#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#define L long long
using namespace std;
const int INF=0x3f3f3f3f;
const int maxn=32;
bool pri[100],vis[100];
int a[35],n;
void init()
{
	memset(pri,1,sizeof(pri));
	pri[0]=0;pri[1]=0;
	for(int i=2;i<=100;i++)
	{
		if(pri[i])
		{
			for(int j=2;j*i<=100;j++)
				pri[j*i]=0;
		}
	}
}
void dfs(int cur)
{
	if(cur==n&&pri[a[n-1]+a[0]])
	{
		printf("%d",a[0]);
		for(int i=1;i