递归返回当前结点是否平衡，和当前深度

# -*- 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):
        def dfs(root):
            if root is None:
                return True, 0
            lf, ld = dfs(root.left)
            rf, rd = dfs(root.right)
            return lf and rf and abs(ld-rd) <= 1, max(ld, rd)+1

        flag, _ = dfs(pRoot)
        return flag