http://poj.org/problem?id=1330

题解：LCA

树上倍增

/*
*@Author:   STZG
*@Language: C++
*/
//#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
#define endl "\n"
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=10000+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,p,l,r,u,v,c;
int ans,cnt,flag,temp,tot,sum,num;
int pre[N];
bool vis[N];
int dep[N];
int dp[N][21];
string str,str1;
struct node{
    int v,w;
}x;
vector<int>G[N];
int find(int x){return pre[x]==x?x:pre[x]=find(pre[x]);}
void marge(int u,int v){
    int tu=find(u);
    int tv=find(v);
    if(tu!=tv){
        pre[tu]=tv;
    }
}
void dfs(int u){
    vis[u]=1;
    for(int i=0,j=G[u].size();i<j;i++){
            int v=G[u][i];
        if(!vis[v]){
            dep[v]=dep[u]+1;
            dp[v][0]=u;
            dfs(v);
        }
    }
}
void init(){
    for(int i=1;i<=n;i++){
       G[i].clear();
       pre[i]=i;
    }
    memset(vis,0,sizeof(vis));
    memset(dep,0,sizeof(dep));
    memset(dp,0,sizeof(dp));
    cnt=0,num=0;
}
int LCA(int x,int y){
    if(dep[x]<dep[y])
        swap(x,y);//cout<<x<<" "<<dp[1][0]<<endl;
    while(dep[x]>dep[y])
        x=dp[x][(int)log2(dep[x]-dep[y])];
    if(x==y)
        return x;

    for(int i=log2(dep[x]);i>=0;i--){
        if(dp[x][i]!=dp[y][i])
            x=dp[x][i],y=dp[y][i];
    }
    return dp[x][0];
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    //cout.tie(0);
    scanf("%d",&t);
    while(t--){
        scanf("%d",&n);
        init();
        for(int i=1;i<n;i++){
            scanf("%d%d",&u,&v);
            G[u].push_back(v);
            G[v].push_back(u);
            marge(v,u);
        }
        //cout<<"1"<<endl;
        for(int i=1;i<=n;i++){
            if(pre[i]==i){
                dfs(i);
            }
        }
        //cout<<"2"<<endl;
        for(int i=0;i<20;i++){
            for(int j=1;j<=n;j++){
                dp[j][i+1]=dp[dp[j][i]][i];
            }
        }
        scanf("%d%d",&u,&v);
        cout<<LCA(u,v)<<endl;
    }

#ifdef DEBUG
	printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
    //cout << "Hello world!" << endl;
    return 0;
}