Heaps: Find the Running Median

Sample Input

6
12
4
5
3
8
7

Sample Output

12.0
8.0
5.0
4.5
5.0
6.0

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

class Heap {
    private Queue<Integer> low = new PriorityQueue<>(Comparator.reverseOrder());
    private Queue<Integer> high = new PriorityQueue<>();

    public void add(int number) {
        Queue<Integer> target = low.size() <= high.size() ? low : high;
        target.add(number);
        balance();
    }

    private void balance() {
        while(!low.isEmpty() && !high.isEmpty() && low.peek() > high.peek()) {
            Integer lowHead= low.poll();
            Integer highHead = high.poll();
            low.add(highHead);
            high.add(lowHead);
        }
    }

    public double median() {
        if(low.isEmpty() && high.isEmpty()) {
            throw new IllegalStateException("Heap is empty");
        } else {
            return low.size() == high.size() ? (low.peek() + high.peek()) / 2.0 : low.peek();
        }
    }
}
public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] a = new int[n];
        Heap heap = new Heap();
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
            heap.add(a[a_i]);
            System.out.println(heap.median());
        }
    }
}