HDU 1272 小希的迷宫

#include <iostream>
#include <cstdio>
#include <cstring>

#define MAX 100000 + 5
using namespace std;

int parent[MAX];
bool used[MAX];

void Make_Set(){
for(int i = 0; i < MAX; i ++ ) parent[i] = i;
}

int Find_Set(int x){
return parent[x] == x ? x : (parent[x]=Find_Set(parent[x]));
}

bool Union_Set(int x,int y){
int a = Find_Set(x), b = Find_Set(y);
if( a == b) return false;
else{
parent[a] = b;
return true;
}
}

int main(){
while(1){
bool isExit = false, isLoop = false;
int a,b;
memset(used,false,sizeof(used));
Make_Set();
while(cin >> a >> b && a && b){
if(a == -1 || b == -1) {isExit  =true;break;}
used[a] = true; used[b] = true;
if(!Union_Set(a,b)) isLoop = true;
}
if(isExit) break;
else if(isLoop) cout<<"No"<<endl;
else{
int cnt = 0;
for(int i = 0 ;i < MAX; i ++ ){
if(used[i] && i == Find_Set(i)) cnt++;
}
if(cnt == 1 || cnt == 0) cout<<"Yes"<<endl;
else cout<<"No"<<endl;
}
}
return 0;
}