Problem URL: N-ary tree postorder traversal

We will traverse the tree with recursive DFS, as it is postorder traversal, we first traverse all the children and then append the root to our result.

"""
# Definition for a Node.
class Node:
    def __init__(self, val=None, children=None):
        self.val = val
        self.children = children
"""

class Solution:
    def postorder(self, root: 'Node') -> List[int]:
        res = []

        def traverse(root, res):
            if not root:
                return 
            for node in root.children:
                traverse(node, res)
            res.append(root.val)

        traverse(root, res)
        return res

Time Complexity: O(n)
Space Complexity: O(n)