776 N Ary Tree Postorder Traversal

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]

 

Constraints:

The number of nodes in the tree is in the range [0, 104].
0 <= Node.val <= 104
The height of the n-ary tree is less than or equal to 1000.

 

Follow up: Recursive solution is trivial, could you do it iteratively?

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

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