## Algorithm

Problem Name: 589. N-ary Tree Preorder Traversal

Given the `root` of an n-ary tree, return the preorder 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: [1,3,5,6,2,4]
```

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: [1,2,3,6,7,11,14,4,8,12,5,9,13,10]
```

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 preorder(Node root) {
if (root == null) {
return new ArrayList<>();
}
List < Integer> list = new ArrayList<>();
Stack stack = new Stack<>();
stack.push(root);
while (!stack.isEmpty()) {
Node popped = stack.pop();
List < Node> children = popped.children;
for (int i = children.size() - 1; i >= 0; i--) {
stack.push(children.get(i));
}
}
return list;
}
}

``````
Copy The Code &

Input

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

Output

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

### #2 Code Example with Javascript Programming

```Code - Javascript Programming```

``````
const preorder = function(root) {
const arr = []
traverse(root, arr)
return arr
};

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

Input

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

Output

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

### #3 Code Example with C# Programming

```Code - C# Programming```

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

namespace LeetCode
{
public class _0589_NAryTreePreorderTraversal
{
public IList < int> Preorder(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)
for (int i = node.children.Count - 1; i >= 0; i--)
stack.Push(node.children[i]);
}

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