uva_615_is it tree

/*
 Author                             :     unlucky_13
 Problem_link                       :
 Category                           :
 Algorithm_Used                     : Got run time error then used map stl and got AC just check the dis-joints sets
 */

#include<cstdio>
#include<sstream>
#include<cstdlib>
#include<cctype>
#include<cmath>
#include<algorithm>
#include<set>
#include<queue>
#include<stack>
#include<list>
#include<iostream>
#include<fstream>
#include<numeric>
#include<string>
#include<vector>
#include<cstring>
#include<map>
#include<iterator>
#define i64 long long int
using namespace std ;
//const long long int inf = 2147483647 ;
//const int minx=;
const int maxn = 1000+10 ;
int par[maxn] ;
int find(int u){
    if(par[u]==u) return u ;
    else return par[u] = find(par[u]) ;
}

int main() {

    freopen("C:\\Users\\Mazhar\\Desktop\\in.txt", "r", stdin);
    int x,y,tree,ct=1,roots,siz,X,Y;
    map<int,int>G ;
    map<int,int>::iterator it;
    while(1){

        scanf("%d %d",&x,&y) ;
        if(x==-1 && y==-1) break ;
        G.clear() ;
        roots = siz = 0 ;
        for(int i=0;i<maxn;i++) par[i]=i ;
        tree=true ;
        while(1){

            if(x==0 && y==0) break ;
            it = G.find(x) ;
            if(it==G.end()){
                G[x]=siz ;
                X = siz ;
                siz++ ;
            }
            else X = it->second ;
            it = G.find(y) ;
            if(it==G.end()){
                G[y]=siz ;
                Y = siz ;
                siz++ ;
            }
            else Y = it->second ;
            int U = find(X) ;
            int V = find(Y) ;
            if(U!=V){
                par[V]=U ;
            }
            else tree = 0 ;

            scanf("%d %d",&x,&y) ;
        }

        //cout<<siz<<endl ;
        for(int i=0;i<siz;i++){
            if(find(i)==i) roots++ ;
        }
        //cout<<roots<<endl ;

        if(roots>1) tree = 0 ;
        if(tree) printf("Case %d is a tree.\n",ct++) ;
        else printf("Case %d is not a tree.\n",ct++) ;

    }


    return 0;
}