hdu 1272 小希的迷宫（并查集判断是否连通）

题目链接：hdu 1272

大概题意：并查集简单运用，用点数 - 边数 == 1 判断是否有环

代码：

#include<cstdio>
#include<cstring>
using namespace std;
#define maxn 100010

int cnt;
int node[maxn];
int vis[maxn];
int F[maxn];
int find(int x)
{
	if(F[x] == -1) return x;
	return F[x] = find(F[x]);
}
void bing(int x, int y)
{
	int p1 = find(x);
	int p2 = find(y);
	if(p1 != p2) F[p1] = p2;
}
int main()
{
	int a, b;
	bool end = false;
	while(true){
		cnt = 0;
		int edge_num  = 0;
		memset(vis, 0, sizeof(vis));
		memset(F, -1, sizeof(F));
		while(true){
			scanf("%d%d", &a, &b);
			if(a == -1 && b == -1){
				end = true;
				break;
			}
			if(a == 0 && b == 0) break;
			if(vis[a] == false){
				vis[a] = true;
				node[cnt] = a; cnt++;
			}
			if(vis[b] == false){
				vis[b] = true;
				node[cnt] = b; cnt++;
			}
			edge_num++;
			bing(a, b);
		}
		if(end) break;
		int rt = find(node[0]);
		bool yeah = true;
		for(int i = 1; i < cnt; i++){
			int v = node[i];
			if(find(v) != rt) {
				yeah = false; break;
			}
		}
		if(yeah && cnt - edge_num == 1)
			printf("Yes\n");
		else if(yeah && cnt == 0)
			printf("Yes\n");
		else printf("No\n");
	}
	return 0;
}