HDU 1272（并查集）

#include<stdio.h>
#include<stdlib.h>
#include<algorithm>
#include<math.h>
#include<string.h>
#include<queue>
#include<vector>
#include<map>
using namespace std;
#define rep(i,n) for(int (i)=1;(i)<=(int)(n);++(i))
const int MAXN=100005;
int from[MAXN],to[MAXN];
int father[MAXN];
int Find(int x)
{
if(x==father[x]) return x;
return father[x]=Find(father[x]);
}
int main()
{
//freopen("test.txt","r",stdin);
int a,b;
int n=0,m=0,cnt=0,ans=0;
while(scanf("%d%d",&a,&b)&&(a!=-1&&b!=-1))
{
father[a]=a,father[b]=b;
if(a&&b)
{
from[++m]=a;to[m]=b;
continue;
}
rep(i,MAXN) if(father[i]==i)n++;
rep(i,m)
{
int ff=Find(from[i]),ft=Find(to[i]);
if(ff==ft) {ans=1;break;}
<span style="white-space:pre">	</span>    else
        {
            father[ff]=ft;
            cnt++;
        }
}
if(!ans&&(cnt==n-1||n==0)) printf("Yes\n");
else printf("No\n");
memset(father,0,sizeof(father));
n=0,m=0,cnt=0,ans=0;
}
return 0;
}