590. N-ary Tree Postorder Traversal - LeetCode Solution

"""
# 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]:
        if not root:
            return []
        a = []
        
        
        def trav(root):
            if not root:
                return 
            
            for i in range(len(root.children)):
                trav(root.children[i])
                a.append(root.children[i].val)
        
        trav(root)
        a.append(root.val)
        return a