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Kth largest element in a stream

Tags : heap, priority-queue, geeksforgeeks, cpp, medium

Problem Statement - link #

Given an input stream of n integers, find the kth largest element each time when an new element is added to the stream.

Your Task: You are required to complete the method kthLargest() which takes 3 arguments and prints kth largest element else -1.

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

Examples #

Example 1:

Input:
k = 4, n = 6
arr[] = {1,2,3,4,5,6}
Output: -1 -1 -1 1 2 3
Explanation: k = 4
For 1, the 4th largest element doesn't
exist so we print -1.
For 2, the 4th largest element doesn't
exist so we print -1.
For 3, the 4th largest element doesn't
exist so we print -1.
For 4, the 4th largest element is 1
{1, 2, 3, 4}
For 5, the 4th largest element is 2
{2, 3, 4 ,5}
For 6, the 4th largest element is 3
{3, 4, 5, 6}

Example 2:

Input:
k = 1, n = 2
arr[] = {3,4}
Output: 3 4

Constraints #

Solutions #

class Solution
{
    public:
    //Function to print kth largest element for each element in the stream.
    void kthLargest(int arr[], int n, int k)
    {
    	// your code here
        priority_queue<int, vector<int>, greater<int>> pq(arr,arr+k);
        for(int i=1; i<k; i++) cout<<-1<<" ";
        for(int i=k; i<n; i++) {
            cout << pq.top() << " ";
            if(pq.top() < arr[i]) { pq.pop(); pq.push(arr[i]); }  

        }
        cout<<pq.top()<< " ";
    }
};