The basic concept of balanced binary tree

The nodes of the binary search tree are inserted in different orders, and there will be different depths and average search lengths ASL.
Balanced binary tree (AVL tree): The absolute value of the height difference between the left and right subtrees of an empty tree or any node does not exceed 1, that is |BF(T)|<=1
balance factor: BF(T)=hL-hR hL and hR is the height of the left and right subtrees of T.

The maximum height of an AVL tree with n nodes is O(log2n)

storage

typedef struct AVLNode *AVLTree;
typedef int ElementType;
struct AVLNode{
    
    
    ElementType Data;
    AVLTree Left; 
    AVLTree Right;  
    int Height;
};