UVa 524 Prime Ring Problem（素数环）

题目链接：UVa 524

题意：

输入正整数n，把正整数1~n组成一个环，使得相邻两个整数之和均为素数。输出时从整数1开始逆时针排列。同一个环应恰好输出一次。n<=16.

分析：

简单BFS.

注意：

两测试案例之间有一行空格，输出数据之间有空格，行末无空格

CODE:

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <string>
#include <algorithm>
#include <queue>
using namespace std;

int prime[40] = { 0,0,1,1,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,0,0,0,0,1,0,1,0,0,0,0,0,1,0,1 };
int n, cases = 0, first = 1;

struct Node {
	int a, cnt;
	int vis[20];
	int num[20];
}cur,nextnode;

void bfs()
{
	queue<Node> q;
	memset(cur.vis, 0, sizeof(cur.vis));
	memset(cur.num, 0, sizeof(cur.num));
	cur.vis[1] = cur.a = cur.cnt = 1;
	cur.num[1] = 1;
	q.push(cur);
	while (!q.empty())
	{
		cur = q.front();
		q.pop();
		for (int i = 2; i <= n; i++)
		{
			if (cur.vis[i] || !prime[cur.a + i]) continue;
			nextnode.a = i;
			nextnode.cnt = cur.cnt + 1;
			for (int j = 1; j <= n; j++)
			{
				nextnode.vis[j] = cur.vis[j];
				nextnode.num[j] = cur.num[j];
			}
			nextnode.vis[i] = 1;
			nextnode.num[nextnode.cnt] = i;
			if (nextnode.cnt == n && prime[nextnode.num
 + 1])
			{
				cout << 1;
				for (int j = 2; j <= n; j++)
					cout << " "<< nextnode.num[j] ;
				putchar('\n');
			}
			q.push(nextnode);
		}
	}
}

int main()
{
#ifdef LOCAL
	freopen("in.txt", "r", stdin);
	//freopen("out.txt", "w", stdout);
#endif
	while (~scanf("%d",&n))
	{
		if (first) first = 0;
		else printf("\n");
		printf("Case %d:\n", ++cases);
		bfs();	
	}
	return 0;
}