路径压缩会爆栈吗，我试了下我画斜线的，可以通过。

/**/
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cctype>
#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <vector>
#include <string>
#include <stack>
#include <queue>

typedef long long LL;
using namespace std;

int u, v;
int f[100005];

// int Find(int x){
// 	return x == f[x] ? x : Find(f[x]);
// }

int Find(int x){
	while(x != f[x]){
		x = f[x];
	}
	return f[x];
}

int main()
{
	//freopen("in.txt", "r", stdin);
	//freopen("out.txt", "w", stdout);

	while(scanf("%d %d", &u, &v) == 2){
		if(u == -1 && v == -1) break;
		for (int i = 1; i <= 100000; i++){
			f[i] = i;
		}
		if(!u && !v){   //坑
			printf("Yes\n");
			continue;
		}
		set<int>st;
		st.insert(u), st.insert(v);
		int x = Find(u), y = Find(v);
		f[x] = y;
		int flag = 0;
		int cnt = 1;
		while(scanf("%d %d", &u, &v) == 2){
			if(u == 0 && v == 0) break;
			x = Find(u), y = Find(v);
			st.insert(u), st.insert(v);
			cnt++;
			if(x != y){
				f[x] = y;
			}else{
				flag = 1;
			}
		}
		(flag || st.size() != cnt + 1) ? printf("No\n") : printf("Yes\n");
	}

	return 0;
}
/**/