Java/src/main/java/com/thealgorithms/misc/MedianOfRunningArray.java

package com.thealgorithms.misc;

import java.util.Collections;
import java.util.PriorityQueue;

/**
 * @author shrutisheoran
 */
public class MedianOfRunningArray {

    private PriorityQueue<Integer> p1;
    private PriorityQueue<Integer> p2;

    // Constructor
    public MedianOfRunningArray() {
        this.p1 = new PriorityQueue<>(Collections.reverseOrder()); // Max Heap
        this.p2 = new PriorityQueue<>(); // Min Heap
    }

    /*
      Inserting lower half of array to max Heap
      and upper half to min heap
     */
    public void insert(Integer e) {
        p2.add(e);
        if (p2.size() - p1.size() > 1) {
            p1.add(p2.remove());
        }
    }

    /*
      Returns median at any given point
     */
    public Integer median() {
        if (p1.size() == p2.size()) {
            return (p1.peek() + p2.peek()) / 2;
        }
        return p1.size() > p2.size() ? p1.peek() : p2.peek();
    }

    public static void main(String[] args) {
        /*
        Testing the median function
         */

        MedianOfRunningArray p = new MedianOfRunningArray();
        int[] arr = { 10, 7, 4, 9, 2, 3, 11, 17, 14 };
        for (int i = 0; i < 9; i++) {
            p.insert(arr[i]);
            System.out.print(p.median() + " ");
        }
    }
}