二叉树非递归后续遍历

一直觉得二叉树的后续遍历非常绕，所以这里就结合自己的感受来阐述一下我的理解

微信图片_20191224113052.jpg

def lastOrder(root):
    if not root:
        return None
    tmp = root
    stack = []
    while tmp or stack:
        while tmp:
            stack.append(tmp)
            tmp = tmp.left
        node = stack[-1]
        tmp = node.right
        if tmp is None:
            node = stack.pop()
            print(node.val)
            while stack and node == stack[-1].right:
                node = stack.pop()
                print(node.val)