FAFU OJ 素数环

素数环

Time Limit:	4000MS	Memory Limit:	65536KB
Total Submissions:	172	Accepted:	79

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Description:

      给定数n，在n的所有排列中，记a[1],a[2],...,a[n]，求满足a[i]+a[i+1](1<=i<=n-1)是素数并且a[1]+a[n]也是素数的所有排列。排列按字典序输出。

Input:

输入只有一行n (0 < n < 20).

Output:

按字典序输出答案

Sample Input:

8

Sample Output:

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

Source:

#include<stdio.h>
#include<iostream>
using namespace std;
#define NO 20
bool prime[]={0,1,1,1,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,0,0,0,0,1,0,1,0,0,0,0,0,1,0,0,0};
bool mark[NO];
int n;
int stack[NO],top;
void print()
{
	printf("%d",stack[0]);
	for(int i=1;i<top;i++)
		printf(" %d",stack[i]);
	puts("");
}
void dfs()
{
	if(top==n)
	{
		if(prime[stack[0]+stack[top-1]])
			print();
		return;
	}
	int i;
	for(i=2;i<=n;i++)
		if(!mark[i]&&prime[stack[top-1]+i])
		{
			mark[i]=1;
			stack[top++]=i;
			dfs();
			top--;
			mark[i]=0;
		}
}
int main()
{
	while(~scanf("%d",&n))
	{
		mark[1]=1;
		stack[top++]=1;
		dfs();
	}
	return 0;
}