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儿子子树的高度最大差别为一，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都是O（log n）。-AVL tree is a self-balancing binary search tree first invented. AVL tree height in any node of the biggest differences between the two sons of a sub-tree, it is a