LeetCode 110. 平衡二叉树

给定一个二叉树，判断它是否是高度平衡的二叉树。
本题中，一棵高度平衡二叉树定义为：
一个二叉树每个节点 的左右两个子树的高度差的绝对值不超过1。

示例 1:
给定二叉树 [3,9,20,null,null,15,7]
    3
   / 
  9  20
    /  
   15   7
返回 true 。

示例 2:
给定二叉树 [1,2,2,3,3,null,null,4,4]
       1
      / 
     2   2
    / 
   3   3
  / 
 4   4
返回 false 。


# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def isBalanced(self, root: TreeNode) -> bool:
        height,isBalanced = self.solver(root)
        return isBalanced


    def solver(self,root):
        if root is None:
            return 0,True
        left_height,left_isBalanced = self.solver(root.left)
        right_height,right_isBalanced = self.solver(root.right)
        height = max(left_height,right_height)+1
        if left_isBalanced is False or right_isBalanced is False or (left_height - right_height)**2 > 1:
            return height,False
        else:
            return height,True