## Algorithm

Problem Name: 590. 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`.

## Code Examples

### #1 Code Example with Java Programming

```Code - Java Programming```

``````
class Solution {
public List postorder(Node root) {
List result = new ArrayList<>();
helper(root, result);
return result;
}

private void helper(Node root, List < Integer> result) {
if (root == null) {
return;
}
for (Node child : root.children) {
helper(child, result);
}
}
}
``````
Copy The Code &

Input

cmd
root = [1,null,3,2,4,null,5,6]

Output

cmd
[5,6,3,2,4,1]

### #2 Code Example with Javascript Programming

```Code - Javascript Programming```

``````
const postorder = function(root) {
const res = []
traverse(root, res)
return res
};

function traverse(node, res) {
if(node == null) return
for(let i = 0; i < node.children.length; i++) {
traverse(node.children[i], res)
}
res.push(node.val>
}
``````
Copy The Code &

Input

cmd
root = [1,null,3,2,4,null,5,6]

Output

cmd
[5,6,3,2,4,1]

### #3 Code Example with C# Programming

```Code - C# Programming```

``````
using System.Collections.Generic;

namespace LeetCode
{
public class _0590_NAryTreePostorderTraversal
{
public IList < int> Postorder(Node root)
{
var result = new List<int>();
if (root == null) return result;

var stack = new Stack < Node>();
stack.Push(root);
while (stack.Count > 0)
{
var node = stack.Pop();
if (node.children != null)
foreach (var child in node.children)
stack.Push(child);
}

result.Reverse();
return result;
}

public class Node
{
public int val;
public IList < Node> children;

public Node() { }

public Node(int _val)
{
val = _val;
}

public Node(int _val, IList < Node> _children)
{
val = _val;
children = _children;
}
}
}
}
``````
Copy The Code &

Input

cmd
root = [1,null,3,2,4,null,5,6]

Output

cmd
[5,6,3,2,4,1]