POJ 1308 Is It A Tree?

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <set>
#include <iterator>
using namespace std;
int father[10002];
int degree[10002]={0};
set<int> V;
void init()
{
int i;
for(i=0;i<10002;i++) {
father[i]=i;
degree[i]=0;
}
}
bool check_one_father(int *f)
{
int i;
int count=0;
set<int>::iterator it=V.begin();
while(it!=V.end()) {
if(father[*it]==*it) {
*f=*it;
count++;
}
it++;
}
if(count!=1)
return false;
return true;
}
bool check_degree(int f)
{
set<int>::iterator it=V.begin();
while(it!=V.end()) {
if(*it==f) {
it++;
continue;
}
else if(degree[*it]!=1)
return false;
it++;
}
return true;
}

bool judge()
{
int fa;
if(!check_one_father(&fa))
return false;
if(degree[fa]!=0)
return false;
if(!check_degree(fa))
return false;
return true;
}
void join(int fa,int chil)
{
father[chil]=fa;
}
int find_father(int chil)
{
if(father[chil]==chil)    return chil;
return find_father(father[chil]);
}
int main()
{
int k=1;
int edge_a,edge_b;
V.clear();
init();
while(scanf("%d%d",&edge_a,&edge_b)!=EOF) {
if(edge_a==edge_b&&edge_a==-1)
return 0;
if(edge_a==edge_b&&edge_a==0) {
if(V.empty()) printf("Case %d is a tree.\n",k++);
else if(judge())
printf("Case %d is a tree.\n",k++);
else
printf("Case %d is not a tree.\n",k++);
init();
V.clear();
} else {
int fa=find_father(edge_a);
join(fa,edge_b);
degree[edge_b]++;//edge_b的入度加1
V.insert(edge_a);
V.insert(edge_b);
}
}
}