# 0590. N-ary Tree Postorder Traversal

<https://leetcode.com/problems/n-ary-tree-postorder-traversal>

## Description

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:**

![](https://assets.leetcode.com/uploads/2018/10/12/narytreeexample.png)

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

**Example 2:**

![](https://assets.leetcode.com/uploads/2019/11/08/sample_4_964.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]
```

**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?

## ac

```java
```