added N-ary Tree Postorder Traversal (easy)

Author: minhyeong-joe

Easy/NaryTreePostorderTraversal/README.md

@@ -0,0 +1,31 @@
+
+# N-ary Tree Postorder Traversal
+[Leetcode Link](https://leetcode.com/problems/n-ary-tree-postorder-traversal/)
+
+## Problem:
+
+Given 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).*
+
+**Follow up:**
+
+Recursive solution is trivial, could you do it iteratively?
+
+## Example:
+
+![example](assets/narytreeexample.png)
+```
+Input: root = [1,null,3,2,4,null,5,6]
+Output: [5,6,3,2,4,1]
+```
+![example](assets/narytreeexample2.png)
+```
+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]
+```
+
+## Note:
+
+- The height of the n-ary tree is less than or equal to `1000`
+- The total number of nodes is between `[0, 10^4]`

Easy/NaryTreePostorderTraversal/assets/narytreeexample.png

@@ -0,0 +1,30 @@
+from typing import List
+
+# Definition for a Node.
+class Node:
+ def __init__(self, val=None, children=None):
+ self.val = val
+ self.children = children
+
+ def __repr__(self):
+ return str(self.val)
+
+class Solution:
+ def postorder(self, root: 'Node') -> List[int]:
+ if root is None:
+ return []
+ postOrder = list()
+ stack = list()
+ stack.append(root)
+ while stack:
+ currentNode = stack.pop()
+ if currentNode.children is not None:
+ stack.extend(currentNode.children) 
+ postOrder.insert(0, currentNode.val)
+ return postOrder
+
+
+# test driver
+sol = Solution()
+tree = Node(1, [Node(3, [Node(5), Node(6)]), Node(2), Node(4)])
+print("Output:", sol.postorder(tree))

Easy/NaryTreePostorderTraversal/assets/narytreeexample2.png

@@ -42,6 +42,7 @@ Languages used: Java and Python
  - [Happy Number](Easy/HappyNumber)
  - [Assign Cookies](Easy/AssignCookies)
  - [Rotate Array](Easy/RotateArray)
+ - [N-ary Tree Postorder Traversal](Easy/NaryTreePostorderTraversal)
 - Medium
  - [Minimum Add to Make Parentheses Valid](Medium/MinimumAddtoMakeParenthesesValid)
  - [Distribute Coins in Binary Tree](Medium/DistributionCoinsInBinaryTree)