小鑫的城堡

#include <bits/stdc++.h>
using namespace std;
int visit[123456];
int pre[123456];
int find(int x)
{
    while(pre[x]!=x)
    {
        x=pre[x];
    }
    return x;
}
void join(int a,int b)
{
    if(find(a)!=find(b))
    {
        pre[find(a)]=find(b);
    }
}
int main()
{
    int m,a,b,i,s1,s2,key;
    while(cin>>m)
    {
        key=m;
        s1=0;
        s2=0;
        memset(visit,0,sizeof(visit));
        for(i=1;i<=123456;i++)
        {
            pre[i]=i;
        }
        while(m--)
        {
            cin>>a>>b;
            join(a,b);
            visit[a]=1;
            visit[b]=1;
        }
        for(i=1;i<=123456;i++)
        {
            if(visit[i]==1)
            {
                s1++;
            }
            if(visit[i]==1&&pre[i]==i)
            {
                s2++;
            }
        }
        if(s1==key+1&&s2==1)
        {
            cout<<"Yes"<<endl;
        }
        else
        {
            cout<<"No"<<endl;
        }
    }
    return 0;
}