输入一棵二叉树，判断该二叉树是否是平衡二叉树。

balancebintree.py

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def IsBalanced_Solution(self, pRoot):
        # write code here
        self.b=True
        self.pre(pRoot)
        return self.b
    def pre(self,tree):
        if tree is None:
            return 0
        l=self.pre(tree.left)
        r=self.pre(tree.right)
        if abs(l-r)>1:
            self.b=False
        return 1+max(l,r)