590_n_ary_tree_postorder_traversal.md

N-ary Tree Postorder Traversal

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

Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)

Example 1:

Input: root = [1,null,3,2,4,null,5,6]
Output: [5,6,3,2,4,1]

Example 2:

Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]

Solution

class Node:
    def __init__(self, val=None, children=None):
        self.val = val
        self.children = children

class Solution:
    def postorder(self, root: 'Node') -> List[int]:
        out = []
        
        def dfs(root):
            if root is None:
                return
            for child in root.children:
                dfs(child)
            out.append(root.val)
        dfs(root)
        return out