poj 1308（据说要用并查集，只用到了路径压缩）

#include<iostream>
#include<cstring>
using namespace std;
#define maxn 10005
int data[maxn],pre[maxn],root[maxn],visit[maxn];
int main(){
    int cnt,i,p,q,rootNum,tmp,nodeNum;
    cnt = 1;
    rootNum = nodeNum = 0;
    bool flag = true;
    memset(data,0,sizeof data);
    memset(pre,0,sizeof pre);
    memset(root,0,sizeof root);
    memset(visit,0,sizeof visit);
    while(scanf("%d%d",&p,&q)==2&&p!=-1){
        if(!p){
            for(int i=0;i<maxn;i++){
                if(!visit[pre[i]]&&pre[i]){
                    tmp = i;
                    while(!visit[pre[tmp]]&&pre[tmp]){
                        tmp = pre[tmp];
                        visit[tmp] = true;
                    }
                    if(!pre[tmp]){
                        root[tmp] = 1;
                    } 
                }
            }
            for(int i=0;i<maxn;i++){
                if(root[i]){
                    rootNum++;
                }
            }
            if(rootNum!=1)flag = false;
            if(!nodeNum)flag = true;
//            for(int i=0;i<maxn;i++){
//                if(data[i]){
//                    cout<<i<<" "<<data[i]<<endl;
//                }
//            }
            if(flag)
                printf("Case %d is a tree.\n",cnt);
            else
                printf("Case %d is not a tree.\n",cnt);
            cnt++;
            rootNum = nodeNum = 0;
            memset(data,0,sizeof data);
            memset(pre,0,sizeof pre);
            memset(root,0,sizeof root);
            memset(visit,0,sizeof visit);

            flag = true;
        }
        else{
            for(i=0;i<maxn;i++){
                if(data[i]==q){
                    flag = false;
                    break;
                }
            }
            if(flag){
                data[p] = q;
                pre[q] = p;
                nodeNum++;
            }
        }
    }
    return 0;
}