二叉树相关的知识点

关于二叉树高度的计算，通过递归的方式得到，跳出递归的条件是，当结点是None的时候，高度为0

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

class Solution:
    def get_height(self, root):
        if root is None:
            return 0
        left_height = self.get_height(root.left)
        right_height = self.get_height(root.right)
        return max(left_height, right_height) + 1