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] = ;
     for(int i =  ; i < vec[u].size() ; i ++){
         int v = vec[u][i];
         if(v == fa) continue;
         dfs(v , u);
     }

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