并查集Is It A Tree?hdu 1325

题目连接http://acm.hdu.edu.cn/showproblem.php?pid=1325

在POJ上WA了，看来还是有问题的呀

#include <iostream>
#include <cstdio>
#include <string.h>
using namespace std;
int hr[100003],hs[100003];
int mer[100003];
int main()
{
   // freopen("in.txt","r",stdin);
    int n,m,i,flag,t=1,cn;

    while(scanf("%d%d",&n,&m))
    {
         if(n<0&&m<0)
           break;
         if(n==0&&m==0)
           {printf("Case %d is a tree.\n",t++);continue;}
         flag=1;cn=0;
        memset(hr,0,sizeof(hr));
        memset(hs,0,sizeof(hs));
        memset(mer,0,sizeof(mer));
         if(hr[n]==0)
            cn++;
         if(hr[m]==0)
           cn++;
            hr[n]=1;
            hr[m]=1;
            hs[m]++;
            mer[m]=n;
            cn--;
        while(scanf("%d%d",&n,&m),n||m)
        {
            if(flag==0)
              continue;
         if(hr[n]==0)
            cn++;
         if(hr[m]==0)
           cn++;
            hr[n]=1;
            hr[m]=1;
            hs[m]++;
            if(hs[m]>1)
              { flag=0;continue;}
            while(mer[n]>0)
              n=mer[n];
            while(mer[m]>0)
              m=mer[m];
            if(m==n)
              { flag=0;continue;}
            mer[m]=n;
            cn--;
        }
        if(flag&&cn!=1)
          flag=0;
          if(flag)
              printf("Case %d is a tree.\n",t++);
          else
              printf("Case %d is not a tree.\n",t++);
    }
    return 0;
}

//去POJ看了下，发现自己漏掉了一种情况（其实有想过这种情况，就是自己以为不会出现，唉）

#include <iostream>
#include <cstdio>
#include <string.h>
using namespace std;
int hr[100003],hs[100003];
int mer[100003];
int main()
{
//freopen("in.txt","r",stdin);
int n,m,i,flag,t=1,cn;

    while(scanf("%d%d",&n,&m))
    {
         if(n<0&&m<0)
           break;
         if(n==0&&m==0)
           {printf("Case %d is a tree.\n",t++);continue;}
         flag=1;cn=0;
        memset(hr,0,sizeof(hr));
        memset(hs,0,sizeof(hs));
        memset(mer,0,sizeof(mer));
         if(hr[n]==0)
            cn++;
         if(hr[m]==0)
           cn++;
         if(m==n)//开始少了这一步、、、树不能自己指向自己呀
           flag=0;
            hr[n]=1;
            hr[m]=1;
            hs[m]++;
            mer[m]=n;
            cn--;
        while(scanf("%d%d",&n,&m),n||m)
        {
            if(flag==0)
              continue;
         if(hr[n]==0)
            cn++;
         if(hr[m]==0)
           cn++;
            hr[n]=1;
            hr[m]=1;
            hs[m]++;
            if(hs[m]>1||m==n)//还有这里，说明hduOJ测试数据还是不怎么强的
              { flag=0;continue;}
            while(mer[n]>0)
              n=mer[n];
            while(mer[m]>0)
              m=mer[m];
            if(m==n)
              { flag=0;continue;}
            mer[m]=n;
            cn--;
        }
        if(flag&&cn!=1)
          flag=0;
          if(flag)
              printf("Case %d is a tree.\n",t++);
          else
              printf("Case %d is not a tree.\n",t++);
    }
    return 0;
}