590. N-ary Tree Postorder Traversal

https://leetcode.com/problems/n-ary-tree-postorder-traversal/

class Solution(object):
    def postorder(self, root):
        """
        :type root: Node
        :rtype: List[int]
        """
        res = []
        if root == None: return res
        stack = [root]
        while stack:
            cur = stack.pop()
            res.append(cur.val)
            stack.extend(cur.children)
        return res[::-1]