桉树的定义来就好了
#include<iostream>
#include<stdio.h>
using namespace std;
int p[100005];
int c[100005];
int u[100005];
int rank[100005];
int father[100005];
int find(int m)
{
if(father[m]==m)
return m;
else
return find(father[m]);
}
void uion(int m,int n)
{
int x,y;
x=find(m);
y=find(n);
if(rank[x]=rank[y])
{
rank[x]++;
father[y]=x;
}
else if(rank[x]>rank[y])
father[y]=x;
else
father[x]=y;
}
int main()
{
int m,n,iii=1,i;
while(scanf("%d%d",&m,&n),m>=0&&n>=0)
{
memset(p,0,sizeof(p));
memset(c,0,sizeof(c));
memset(u,-1,sizeof(u));
memset(rank,0,sizeof(rank));
for(i=0;i<100005;i++)
father[i]=i;
p[m]=1;
p[n]=1;
u[n]=m;
c[n]++;
uion(m,n);
while(scanf("%d%d",&m,&n),m||n)
{
p[m]=1;
p[n]=1;
if(u[n]!=m)
{
c[n]++;
u[n]=m;
}
uion(m,n);
}
int sum=0,sum1=0,sum2=0;
int m=-1;
for(i=0;i<100005;i++)
{
if(p[i]==1&&find(i)!=m)
{
m=find(i);
sum2++;
}
if(p[i]==1&&c[i]!=1)
sum++;
if(p[i]==1&&c[i]==0)
sum1++;
}
if(sum==1&&sum1==1&&sum2==1)
printf("Case %d is a tree.\n",iii++);
else
printf("Case %d is not a tree.\n",iii++);
}
}