avl树的实现：

avl树是每个节点的左子树和右子树的高度最多差1的二叉查找树.一棵高度为h的avl树最少节点数由S(h) = S(h-1)+S(h-2)+1得到.avl树要保证任一节点的左右子树的高度之差的绝对值不能超过1(空树的高定义为1).在插入和删除的时候就需要根据情况对树的某些节点做调整-AVL tree realization: avl tree is left to each node subtree and right subtree height difference up to 1 binary search tree. a height of at least h of AVL tree nodes from S (h) = S (h-1)+ S (h-2)+ 1 received. avl tree to ensure that any one node subtree about the difference between the height of the absolute value of not more than one (empty tree for high-definition 1). in the insertion and deleted when you need according to the circumstances of the tree node to do some adjustments