Leetcode590. N-ary Tree Postorder Traversal

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