UVA524 PrimeRingProblem素数环

输入正整数n，把整数1，2，3，···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。n16。

回溯法

#include<iostream>
#include <string>
#include <string.h>
#include<math.h>

using namespace std;
int vis[16+5]; int n; int tot = 0; int c[16+5]; int isp[40];
void dfs(int cur) {
	if (cur == n && isp[c[0] + c[n - 1]]) {
		for (int i = 0; i < n-1; i++)cout << c[i] << " ";
		cout << c[n - 1];
		cout << endl;
	}else
	for (int i = 2; i <= n; i++) {
		if (!vis[i] && isp[c[cur-1] + i]) {//头节点是确定的
			vis[i] = 1;
			c[cur] = i;
			dfs(cur + 1);
			vis[i] = 0;   //循环遍历每一种情况
		}
	}
}
int main()
{
#ifdef LOCAL
	freopen("data.in", "r", stdin);//scanf
	freopen("data.out", "w", stdout);//printf
#endif
	int kase = 0;
	
	for (int i = 1; i <= 2 * 16; i++) {
		bool isok = true;
		for (int j = 2; j <= sqrt(i); j++) {
			if (i%j == 0)isok = false;
		}
		if (isok)isp[i] = 1;
	}
	while (scanf("%d", &n)==1&&n) {
                if(kase)cout<<endl;
		kase++;
		cout << "Case " << kase << ":"<<endl;
		memset(vis, 0, sizeof(vis));
		memset(c, 0, sizeof(c));
		c[0] = 1;
		dfs(1);
		//cout << endl;
	}
	//system("pause");
	return 0;
}