Clone N-ary Tree
<p>Given a <code>root</code> of an N-ary tree, return a <a href="https://en.wikipedia.org/wiki/Object_copying#Deep_copy" target="_blank"><strong>deep copy</strong></a> (clone) of the tree.</p>

<p>Each node in the n-ary tree contains a val (<code>int</code>) and a list (<code>List[Node]</code>) of its children.</p>

<pre>
class Node {
    public int val;
    public List&lt;Node&gt; children;
}
</pre>

<p><em>Nary-Tree input serialization is represented in their level order traversal, each group of children is separated by the null value (See examples).</em></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<p><img src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1400-1499/1490.Clone%20N-ary%20Tree/images/narytreeexample.png" style="width: 100%; max-width: 300px;" /></p>

<pre>
<strong>Input:</strong> root = [1,null,3,2,4,null,5,6]
<strong>Output:</strong> [1,null,3,2,4,null,5,6]
</pre>

<p><strong class="example">Example 2:</strong></p>

<p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1400-1499/1490.Clone%20N-ary%20Tree/images/sample_4_964.png" style="width: 296px; height: 241px;" /></p>

<pre>
<strong>Input:</strong> 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]
<strong>Output:</strong> [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]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The depth of the n-ary tree is less than or equal to <code>1000</code>.</li>
	<li>The total number of nodes is between <code>[0, 10<sup>4</sup>]</code>.</li>
</ul>

<p>&nbsp;</p>
<strong>Follow up: </strong>Can your solution work for the <a href="https://leetcode.com/problems/clone-graph/" target="_blank">graph problem</a>?
Tree; Depth-First Search; Breadth-First Search; Hash Table
/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> children;

    Node() {}

    Node(int _val) {
        val = _val;
    }

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/

class Solution {
public:
    Node* cloneTree(Node* root) {
        if (!root) {
            return root;
        }
        vector<Node*> children;
        for (Node* child : root->children) {
            children.emplace_back(cloneTree(child));
        }
        return new Node(root->val, children);
    }
};