Binary Tree Inorder Traversal

Given the root of a binary tree, return the inorder traversal of its nodes' values.

Example 1:

Input: root = [1,null,2,3]
Output: [1,3,2]

Example 2:

Input: root = []
Output: []

Example 3:

Input: root = [1]
Output: [1]

Solution:

"""
前序遍历：打印 - 左 - 右
中序遍历：左 - 打印 - 右
后序遍历：左 - 右 - 打印
"""
class Solution(object):
	def inorderTraversal(self, root):
		res = []
		def dfs(root):
			if not root:
				return
			# 按照 左-打印-右的方式遍历	
			dfs(root.left)
			res.append(root.val)
			dfs(root.right)
		dfs(root)
		return res