590. 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 postorderHelp(self,root,path):
        if root is None:
            return
        children = root.children
        for ch in children:
            self.postorderHelp(ch,path)
        path.append(root.val)

    def postorder(self, root):
        """
        :type
        root: Node
        :rtype: List[int]
        """
        re_li = []
        self.postorderHelp(root,re_li)
        return re_li