HDU2094---产生冠军

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<math.h>
#include<set>
#include<iostream>
#include<stdlib.h>
#include<string>
#include<set>
#include<map>
using namespace std;
int n,m;
set<string>Set1;
set<string>Set2;
int main()
{
    int n;
    while(scanf("%d",&n)&&n){
        Set1.clear();
        Set2.clear();
    string a,b;
    int k=1,u,v;
    for(int ii=1;ii<=n;ii++){
        cin>>a>>b;
        Set1.insert(a);
        Set1.insert(b);
        Set2.insert(b);
    }

    if(Set1.size()==Set2.size()+1)
        printf("Yes\n");
    else printf("No\n");
    }
}