JavaAlgorithms/Misc/MedianOfRunningArray.java

package 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() + " ");
    }
  }
}