589. N-ary Tree Preorder Traversal

Given an n-ary tree, return the preorder traversal of its nodes' values.

For example, given a 3-ary tree:

Return its preorder traversal as: [1,3,5,6,2,4].

# Definition for a Node.
class Node(object):
    def __init__(self, val, children):
        self.val = val
        self.children = children



class Solution(object):
    def preorder(self, root):
        """
        :type root: Node
        :rtype: List[int]
        """
        res = []
        if not root:
            return []
        res.append(root.val)
        for child in root.children:
            res.extend(self.preorder(child))
        return res