Kth Largest Sum in a Binary Tree
<p>You are given the <code>root</code> of a binary tree and a positive integer <code>k</code>.</p>

<p>The <strong>level sum</strong> in the tree is the sum of the values of the nodes that are on the <strong>same</strong> level.</p>

<p>Return<em> the </em><code>k<sup>th</sup></code><em> <strong>largest</strong> level sum in the tree (not necessarily distinct)</em>. If there are fewer than <code>k</code> levels in the tree, return <code>-1</code>.</p>

<p><strong>Note</strong> that two nodes are on the same level if they have the same distance from the root.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/2500-2599/2583.Kth%20Largest%20Sum%20in%20a%20Binary%20Tree/images/binaryytreeedrawio-2.png" style="width: 301px; height: 284px;" />
<pre>
<strong>Input:</strong> root = [5,8,9,2,1,3,7,4,6], k = 2
<strong>Output:</strong> 13
<strong>Explanation:</strong> The level sums are the following:
- Level 1: 5.
- Level 2: 8 + 9 = 17.
- Level 3: 2 + 1 + 3 + 7 = 13.
- Level 4: 4 + 6 = 10.
The 2<sup>nd</sup> largest level sum is 13.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/2500-2599/2583.Kth%20Largest%20Sum%20in%20a%20Binary%20Tree/images/treedrawio-3.png" style="width: 181px; height: 181px;" />
<pre>
<strong>Input:</strong> root = [1,2,null,3], k = 1
<strong>Output:</strong> 3
<strong>Explanation:</strong> The largest level sum is 3.
</pre>

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

<ul>
	<li>The number of nodes in the tree is <code>n</code>.</li>
	<li><code>2 &lt;= n &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= Node.val &lt;= 10<sup>6</sup></code></li>
	<li><code>1 &lt;= k &lt;= n</code></li>
</ul>
Tree; Breadth-First Search; Binary Tree; Sorting
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    long long kthLargestLevelSum(TreeNode* root, int k) {
        vector<long long> arr;
        queue<TreeNode*> q{{root}};
        while (!q.empty()) {
            long long t = 0;
            for (int n = q.size(); n; --n) {
                root = q.front();
                q.pop();
                t += root->val;
                if (root->left) {
                    q.push(root->left);
                }
                if (root->right) {
                    q.push(root->right);
                }
            }
            arr.push_back(t);
        }
        if (arr.size() < k) {
            return -1;
        }
        sort(arr.rbegin(), arr.rend());
        return arr[k - 1];
    }
};