【POJ 1330】Nearest Common Ancestors(最近公共祖先)

/* ***********************************************
Author        :Torrance_ZHANG
Created Time  :2016/4/29 22:11:34
File Name     :ceshi2.cpp
************************************************ */

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>
typedef long long int LL;
using namespace std;
const int MAXN=10010;
int qx,qy,res;
struct Edge{
    int to;
    int next;
    Edge(){
        to=-1;
        next=-1;
    }
}edge[MAXN];
int deg[MAXN];              //统计入度，找根
int n,cnt,head[MAXN],fa[MAXN],rnk[MAXN],vis[MAXN];      //rnk统计节点的秩，即深度
void add(int u,int v){
    edge[cnt].to=v;
    edge[cnt].next=head[u];
    head[u]=cnt;
    cnt++;
}
int Find(int x){
    return x==fa[x]?fa[x]:fa[x]=Find(fa[x]);
}
void Tarjan(int x){
    fa[x]=x;
    for(int i=head[x];i!=-1;i=edge[i].next){
        Tarjan(edge[i].to);
        fa[edge[i].to]=x;
    }
    if(x==qx||x==qy){
        if(x!=qx) swap(qx,qy);
        if(fa[qy])
            res=Find(fa[qy]);
    }
}
int main(){
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    int t;
    scanf("%d",&t);
    while(t--){
        cnt=0;
        res=0;
        memset(head,-1,sizeof(head));
        memset(deg,0,sizeof(deg));
        memset(fa,0,sizeof(fa));
        scanf("%d",&n);
        for(int i=1;i<n;i++){
            int x,y;
            scanf("%d%d",&x,&y);
            add(x,y);
            deg[y]++;
        }
        int root=0;
        scanf("%d%d",&qx,&qy);
        for(int i=1;i<=n;i++){
            if(deg[i]==0){
                root=i;
                break;
            }
        }
        Tarjan(root);
        printf("%d\n",res);
    }
    return 0;
}