KthLargestEleInStream.java

/*
You are part of a university admissions office and need to keep track of the kth highest test score from applicants in real-time. This helps to determine cut-off marks for interviews and admissions dynamically as new applicants submit their scores.

You are tasked to implement a class which, for a given integer k, maintains a stream of test scores and continuously returns the kth highest test score after a new score has been submitted. More specifically, we are looking for the kth highest score in the sorted list of all scores.

Implement the KthLargest class:
KthLargest(int k, int[] nums) Initializes the object with the integer k and the stream of test scores nums.
int add(int val) Adds a new test score val to the stream and returns the element representing the kth largest element in the pool of test scores so far.
 
Example 1:

Input:
["KthLargest", "add", "add", "add", "add", "add"]
[[3, [4, 5, 8, 2]], [3], [5], [10], [9], [4]]

Output: [null, 4, 5, 5, 8, 8]
Explanation:
KthLargest kthLargest = new KthLargest(3, [4, 5, 8, 2]);
kthLargest.add(3); // return 4
kthLargest.add(5); // return 5
kthLargest.add(10); // return 5
kthLargest.add(9); // return 8
kthLargest.add(4); // return 8
*/ 
class KthLargest {
    PriorityQueue<Integer> minPQ;
    int k;
    public KthLargest(int k, int[] nums) {
        this.k = k;
        minPQ = new PriorityQueue<>();
        for(int num : nums){
            minPQ.offer(num);
            if(minPQ.size() > k)
                minPQ.poll(); //so that kth largest element is always at root
        }
    }
    
    public int add(int val) {
        minPQ.offer(val);
        if(minPQ.size() > k)
            minPQ.poll();
        return minPQ.peek();
    }
}