N-ary Tree Level Order Traversal
<p>Given an n-ary tree, return the <em>level order</em> traversal of its nodes&#39; values.</p>

<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/0400-0499/0429.N-ary%20Tree%20Level%20Order%20Traversal/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],[3,2,4],[5,6]]
</pre>

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

<p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0400-0499/0429.N-ary%20Tree%20Level%20Order%20Traversal/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],[2,3,4,5],[6,7,8,9,10],[11,12,13],[14]]
</pre>

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

<ul>
	<li>The height 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>
Tree; Breadth-First Search
/**
 * Definition for node.
 * class Node {
 *     val: number
 *     children: Node[]
 *     constructor(val?: number) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.children = []
 *     }
 * }
 */

function levelOrder(root: Node | null): number[][] {
    const ans: number[][] = [];
    if (!root) {
        return ans;
    }
    const q: Node[] = [root];
    while (q.length) {
        const qq: Node[] = [];
        const t: number[] = [];
        for (const { val, children } of q) {
            qq.push(...children);
            t.push(val);
        }
        ans.push(t);
        q.splice(0, q.length, ...qq);
    }
    return ans;
}
