N-ary Tree Preorder Traversal.py

'''
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].
 

Note: Recursive solution is trivial, could you do it iteratively?
'''

"""
# 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
        
        res.append(root.val)
        if root.children:
            for x in root.children:
                res.extend(self.preorder(x))
        
        return res