扩展AVLTree，添加克隆，合并和打印方法-extend the AVLTree class to include the following methods: clone(AVLTree<K,V> tree)；merge(AVLTree<K,V> tree1, AVLTree<K,V> tree2 )；void print(AVLTree<K, V>)

平衡二叉树的实现以及算法测试，通过java语言实现的。-Balanced binary tree algorithm implementation and testing by java language.