题目地址
An AVL tree is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property. Figures 1-4 illustrate the rotation rules.

Now given a sequence of insertions, you are supposed to tell the root of the resulting AVL tree.
Input Specification:
Each input file contains one test case. For each case, the first line contains a positive integer N (≤20) which is the total number of keys to be inserted. Then N distinct integer keys are given in the next line. All the numbers in a line are separated by a space.

Output Specification:
For each test case, print the root of the resulting AVL tree in one line.

Sample Input 1:
5
88 70 61 96 120

Sample Output 1:
70

Sample Input 2:
7
88 70 61 96 120 90 65

Sample Output 2:
88

#include <iostream>
#include <vector>
#include<algorithm>
#include <cmath>
#include<map>
#include<cstring>
#include<queue>
#include<string>
#include<set>
#include<stack>
using namespace std;
typedef long long ll;
const int maxn=110,inf=100000000;
struct node{
    int data,height;
    node *lchild,*rchild;
};
int a[maxn],n;
int get_height(node* root){
    if(root==NULL) return 0;
    return root->height;
}
void update(node *&root){
    root->height=max(get_height(root->lchild),get_height(root->rchild))+1;
}
int get_fac(node *root){
    return get_height(root->lchild)-get_height(root->rchild);
}
void l(node* &root){
    node *temp=root->rchild;
    root->rchild=temp->lchild;
    temp->lchild=root;
    update(root);update(temp);
    root=temp;
}
void r(node *&root){
    node* temp=root->lchild;
    root->lchild=temp->rchild;
    temp->rchild=root;
    update(root);update(temp);
    root=temp;
}
void insert(node *&root,int data){
    if(!root){
        root=new node;
        root->data=data;
        root->height=1;
        root->lchild=root->rchild=NULL;
        return;
    }
    if(data<root->data){
        insert(root->lchild,data);
        update(root);
        if(get_fac(root)==2){
            if(get_fac(root->lchild)==1) r(root);
            else{
                l(root->lchild);r(root);
            }
        }
    }
    else{
        insert(root->rchild,data);
        update(root);
        if(get_fac(root)==-2){
            if(get_fac(root->rchild)==-1) l(root);
            else{
                r(root->rchild);l(root);
            }
        }
    }
}
int main(){
    cin>>n;node *root=NULL;
    for(int i=0;i<n;i++) {
        cin>>a[i];
        insert(root,a[i]);
    }
    cout<<root->data;
}