问题描述：

python：

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):def inorder(self, root):if not root:returnself.inorder(root.left)    # leftself.res.append(root.val)  # rootself.inorder(root.right)   # rightdef inorderTraversal(self, root):""":type root: TreeNode:rtype: List[int]"""self.res = list()self.inorder(root)return self.res