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

For example:

Given binary tree {1,#,2,3},

比较简单，就是转化成中序遍历即可，访问顺序是中序遍历左子树，根节点，中序遍历右子树

Python编程的时候需要注意，要在返回单一数字的时候加上中括号【】，否则Python不知道这是一个list

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

class Solution:
    # @param root, a tree node
    # @return a list of integers
    def inorderTraversal(self, root):
        if root is None:
            return []
        elif root.left is None and root.right is None:
            return [root.val]
        else:
            return self.inorderTraversal(root.left)+[root.val]+self.inorderTraversal(root.right)