两个测试点超时
22分

版本1

#include<bits/stdc++.h>
using namespace std;
struct node{
	int x;
	node* left;
	node* right;
};
//在线建树很费时 
void create(node* &root,int v){
	if(root == NULL){
		root = new node;
		root->x = v;
		root->left = root->right = NULL;
		return;
	}else if(root->x <= v){
		create(root->right, v);
	}else create(root->left, v);
}
//深搜 
void dfs(node* root, int u, int v, int f){
	if(root == NULL) return;
	
	if(root->x == u){
		printf("%d is an ancestor of %d.\n", u,v);
		return;
	}else if(root->x == v){
		printf("%d is an ancestor of %d.\n", v,u);
		return;
	}else if(root->x > u && root->x < v){
		if(f) swap(u,v); //交换过的，要换回来再输出，不然是反的 
		printf("LCA of %d and %d is %d.\n", u, v, root->x);
		return;
	}else if(root->x >u && root->x > v) dfs(root->left,u,v,f);
	else dfs(root->right,u,v,f);
}
map<int, bool> mp;
int main(){
	int n,m,x,y;
	scanf("%d%d",&n,&m);
	node* root=NULL;
	for(int i=0;i<m;i++){
		scanf("%d",&x);
		mp[x]=true;
		create(root, x);
	}
	
	for(int i=0;i<n;i++){
		scanf("%d%d",&x,&y);
		if(mp[x]==false && mp[y]==false) printf("ERROR: %d and %d are not found.\n", x, y);
		else if(mp[x]==false)  printf("ERROR: %d is not found.\n", x);
		else if(mp[y]==false)  printf("ERROR: %d is not found.\n", y);
		else{
			bool flag = false;
			if(x > y){
				flag = true;
				swap(x, y);
			}
			dfs(root, x, y, flag);
		}
	}
	
	return 0;
}

版本2

柳婼大神

#include <iostream>
#include <vector>
#include <map>
using namespace std;
map<int, bool> mp;
int main() {
    int m, n, u, v, a;
    scanf("%d %d", &m, &n);
    vector<int> pre(n);
    for (int i = 0; i < n; i++) {
        scanf("%d", &pre[i]);
        mp[pre[i]] = true;
    }
    for (int i = 0; i < m; i++) {
        scanf("%d %d", &u, &v);
        for(int j = 0; j < n; j++) {
            a = pre[j];
            if ((a >= u && a <= v) || (a >= v && a <= u)) break;
        } 
        if (mp[u] == false && mp[v] == false)
            printf("ERROR: %d and %d are not found.\n", u, v);
        else if (mp[u] == false || mp[v] == false)
            printf("ERROR: %d is not found.\n", mp[u] == false ? u : v);
        else if (a == u || a == v)
            printf("%d is an ancestor of %d.\n", a, a == u ? v : u);
        else
            printf("LCA of %d and %d is %d.\n", u, v, a);
    }
    return 0;
}

版本3

可以通过！

#include<bits/stdc++.h>
using namespace std;
const int maxn=1e4+5;
map<int, bool> mp;
int pre[maxn],in[maxn];
struct node{
	int x;
	node* left;
	node* right;
};
//离线建树好一点 
void create(node* &root, int preL, int preR, int inL, int inR){
	if(preL > preR ) return;
	root = new node; //很关键 
	root->x = pre[preL];
	root->left = root->right =NULL;
	int k=inL;
	while(in[k] != pre[preL]){
		k++;
	}
	int tmp = k - inL;
	create(root->left,preL+1, preL+tmp, inL, k-1);
	create(root->right,preL+tmp+1, preR, k+1, inR);
	
}
void inorder(node* root){
	if(root == NULL) return;
	inorder(root->left);
	cout<<root->x<<" ";
	inorder(root->right);
}
//深搜 
void dfs(node* root, int u, int v, int f){
	if(root == NULL) return;
	
	if(root->x == u){
		printf("%d is an ancestor of %d.\n", u,v);
		return;
	}else if(root->x == v){
		printf("%d is an ancestor of %d.\n", v,u);
		return;
	}else if(root->x > u && root->x < v){
		if(f) swap(u,v); //交换过的，要换回来再输出，不然是反的 
		printf("LCA of %d and %d is %d.\n", u, v, root->x);
		return;
	}else if(root->x >u && root->x > v) dfs(root->left,u,v,f);
	else dfs(root->right,u,v,f);
}

int main(){
	int n,m,x,y;
	node* root = NULL;
	scanf("%d%d",&n,&m);
	for(int i=0;i<m;i++){
		scanf("%d",&x);
		in[i]=x;
		pre[i]=x;
		mp[x]=true;
	}
	sort(in,in+m);
	create(root,0, m-1, 0, m-1);

	for(int i=0;i<n;i++){
		scanf("%d%d",&x,&y);
		if(mp[x]==false && mp[y]==false) printf("ERROR: %d and %d are not found.\n", x, y);
		else if(mp[x]==false)  printf("ERROR: %d is not found.\n", x);
		else if(mp[y]==false)  printf("ERROR: %d is not found.\n", y);
		else{
			bool flag = false;
			if(x > y){
				flag = true;
				swap(x, y);
			}
			dfs(root, x, y, flag);
		}
	}
	
	return 0;
}