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 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:
    vector<vector<int>> levelOrder(Node* root) {
        vector<vector<int>> ans;
        if (!root) {
            return ans;
        }
        queue<Node*> q{{root}};
        while (!q.empty()) {
            vector<int> t;
            for (int n = q.size(); n; --n) {
                root = q.front();
                q.pop();
                t.push_back(root->val);
                for (auto& child : root->children) {
                    q.push(child);
                }
            }
            ans.push_back(t);
        }
        return ans;
    }
};