leetcode 94. Binary Tree Inorder

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

Input: [1,null,2,3]
   1
    \
     2
    /
   3

Output: [1,3,2]

Follow up: Recursive solution is trivial, could you do it iteratively?

解法和leetcode144类似
就是利用递归求中序遍历。
python代码：

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

class Solution:
    def inorderTraversal(self, root: TreeNode) -> List[int]:
        nums = []
        if not root:
            return []
        nums.extend(self.inorderTraversal(root.left))
        nums.append(root.val)
        nums.extend(self.inorderTraversal(root.right))
        return nums