LCA 最近公共祖先 （模板）

#include <iostream>
#include <stdio.h>
#include <cstring>
#include <vector>
#define N 100005
using namespace std;
vector <int> vec[N] ;
vector <pair<int,int> > query[N];
struct node{
    int first , second;
}e;

vector <node> query[N];

int vis[N] , pre[N] , ans[N];
int Find(int x){
    if(pre[x] == x){
        return x;
    }else{
        pre[x] = Find(pre[x]);
        return pre[x];
    }
}
void dfs(int u , int fa){
    
    pre[u] = u;
    vis[u] = 1;
    for(int i = 0 ; i < vec[u].size() ; i ++){
        int v = vec[u][i];
        if(v == fa) continue;
        dfs(v , u);
    }
    
    for(int i = 0 ; i < query[u].size() ; i++){
        int v = query[u][i].first;
        int id = query[u][i].second;
        if(vis[v] == 1){
            ans[id] = Find(v);
        }
    }

    pre[u] = fa;
}

int main(){
    int T;
    scanf("%d" ,&T);
    while(T --){
        int n , x, y;
        scanf("%d" , &n);
        for(int i = 0 ; i < n - 1 ; i ++){
            scanf("%d%d" , &x , &y);
            vec[x].push_back(y);
            vec[y].push_back(x);
            vis[y] = 1;
        }
        for(int i = 1 ; i <= n ; i ++ ){
            cout << i << "==========" << endl;
            for(int k = 0 ; k  <  vec[i].size() ; k ++){
                cout << vec[i][k] << " ";
            }
            cout << endl;
        }
        int q;
        scanf("%d",&q);
        for(int i = 0 ; i < q ; i ++){
            scanf("%d%d" , &x , &y);
            query[x].push_back({y , i});
            query[y].push_back({x , i});
        }
        for(int i = 1 ; i <= n ; i ++){
            if(vis[i] == 0){
                memset(vis , 0 ,sizeof(vis));
                dfs(i , -1);
                break;
            }
        }
        for(int i = 0 ; i < q ; i ++){
            printf("%d\n" ,ans[i]);
        }
    }
}