给出一棵二叉树，返回其节点值的后序遍历。

2017.11.15

2017.11.16

"""
Definition of TreeNode:
class TreeNode:
    def __init__(self, val):
        self.val = val
        self.left, self.right = None, None
"""


class Solution:
    """
    @param: root: A Tree
    @return: Postorder in ArrayList which contains node values.
    """
    a = []
    def postorderTraversal(self, root):
        # write your code here
        self.left(root)
        return self.a
    def left(self,root):
        if root == None:
            return
        self.left(root.left)
        self.right(root.right)
        self.a.append(root.val)
    def right(self,root):
        if root == None:
            return
        self.left(root.left)
        self.right(root.right)
        self.a.append(root.val)