1066 Root of AVL Tree（25分）

代码如下：

#include<bits/stdc++.h>
using namespace std;
struct node{
    int val;
    node *left, *right;
    node(int v):val(v){
        left = nullptr;
        right = nullptr;
    }
};
int getHeight(node *root){
    if(root == nullptr)
        return 0;
    return max(getHeight(root->left),getHeight(root->right)) + 1;
}
node *rotateLeft(node *root){
    node *t = root->right;
    root->right = t->left;
    t->left = root;
    return t;
}
node *rotateRight(node *root){
    node *t = root->left;
    root->left = t->right;
    t->right = root;
    return t;
}
node *rotateLeftRight(node *root){
    root->left = rotateLeft(root->left);
    return rotateRight(root);
}
node *rotateRightLeft(node *root){
    root->right = rotateRight(root->right);
    return rotateLeft(root);
}
node *insert(node *root, int val){
    if(root == nullptr)
        root = new node(val);
    else if(val < root->val){
        root->left = insert(root->left,val);
        if(getHeight(root->left) - getHeight(root->right) == 2)
            root = val < root->left->val ? rotateRight(root) : rotateLeftRight(root);
    }
    else{
        root->right = insert(root->right,val);
        if(getHeight(root->right) - getHeight(root->left) == 2)
            root = val > root->right->val ? rotateLeft(root) : rotateRightLeft(root);
    }
    return root;
}
int main(){
    int N, val;
    cin>>N;
    node *root = nullptr;
    for(int i = 0; i < N; i++){
        cin>>val;
        root = insert(root,val);
    }
    cout<<root->val;
    return 0;
}

参考了柳神的代码后，我被大佬折服了，写的太妙了这个AVL。
笔记：
1、AVL的左右旋 = 中间结点的左旋 + 最上面结点的右旋
2、AVL的右左旋 = 中间结点的右旋 + 最上面结点的左旋