# -*- coding: utf-8 -*-

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

class Solution(object):
    def postorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if not root:
            return []
        
        result = []
        
        def postorder(node, result):
            if node.left:
                postorder(node.left, result)
            if node.right:
                postorder(node.right, result)
            result.append(node.val)
        
        postorder(root, result)
        
        return result
        
