kth_largest-sum_in_binarytree.cpp

// Problem Link :https://leetcode.com/problems/kth-largest-sum-in-a-binary-tree/description/

/**
 * 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) {

        if (root == NULL) {
        return (k == 0) ? 0 : -1;
    }  
    queue<TreeNode*> q;
    priority_queue<long long> pq;
    q.push(root);

    while (!q.empty()) {
        int n = q.size();
        long long sum = 0;
        for (int i = 0; i < n; ++i) {
            TreeNode* curr = q.front();
            q.pop();
            sum += curr->val;

            if (curr->left) {
                q.push(curr->left);
            }

            if (curr->right) {
                q.push(curr->right);
            }
        }

        pq.push(sum);
    }
    if (pq.size() < k) {
        return -1;
    }
    for (int i = 1; i < k; ++i) {
        pq.pop();
    }
    return pq.top();
    }
};