k largest elements.cpp

/*
k largest elements
==================

Given an array Arr of N positive integers, find K largest elements from the array.  The output elements should be printed in decreasing order.

Example 1:
Input:
N = 5, K = 2
Arr[] = {12, 5, 787, 1, 23}
Output: 787 23
Explanation: 1st largest element in the
array is 787 and second largest is 23.

Example 2:
Input:
N = 7, K = 3
Arr[] = {1, 23, 12, 9, 30, 2, 50}
Output: 50 30 23
Explanation: 3 Largest element in the
array are 50, 30 and 23.
Your Task:
You don't need to read input or print anything. Your task is to complete the function kLargest() which takes the array of integers arr, n and k as parameters and returns an array of integers denoting the answer. The array should be in decreasing order.

Expected Time Complexity: O(N)
Expected Auxiliary Space: O(K*logK)

Constraints:
1 ≤ K ≤ N ≤ 105
1 ≤ Arr[i] ≤ 106
 
*/

vector<int> kLargest(int arr[], int n, int k)
{
  vector<int> ans;
  priority_queue<int> pq;
  for (int i = 0; i < n; ++i)
    pq.push(arr[i]);

  for (int i = 0; i < k; ++i)
  {
    ans.push_back(pq.top());
    pq.pop();
  }

  return ans;
}