说明：  在计算机科学中，AVL树是最先发明的自平衡二叉查找树。在AVL树中任何节点的两个子树的高度最大差别为1，所以它也被称为高度平衡树。查找、插入和删除在平均和最坏情况下的时间复杂度都是。增加和删除可能需要通过一次或多次树旋转来重新平衡这个树。
(In computer science, AVL tree is the first self balanced binary search tree. In AVL tree, the maximum height difference between two subtrees of any node is 1, so it is also called height balance tree. The time complexity of find, insert, and delete in average and worst cases is. Adding and deleting may require rebalancing the tree by one or more tree rotations.)