题目链接：https://leetcode-cn.com/problems/ping-heng-er-cha-shu-lcof/
难度：简单

描述：
输入一棵二叉树的根节点，判断该树是不是平衡二叉树。如果某二叉树中任意节点的左右子树的深度相差不超过1，那么它就是一棵平衡二叉树。

题解

  1. # Definition for a binary tree node.
  2. # class TreeNode:
  3. #     def __init__(self, x):
  4. #         self.val = x
  5. #         self.left = None
  6. #         self.right = None
  8. class Solution:
  9.     def isBalanced(self, root: TreeNode) -> bool:
  10.         def recursion(root):
  11.             if root is None:
  12.                 return 0
  13.             left_depth = recursion(root.left)
  14.             if left_depth == -1:
  15.                 return -1
  17.             right_depth = recursion(root.right)
  18.             if right_depth == -1:
  19.                 return -1
  21.             if abs(left_depth - right_depth) < 2:
  22.                 return max(left_depth, right_depth) + 1
  23.             else:
  24.                 return -1
  26.         return recursion(root) != -1