Find Median from Data Stream

Javascript (ES6)

class RunningMedian {
  minHeap = new MinHeap();
  maxHeap = new MaxHeap();

  add = (val) => {
    maxHeap.add(val);
    minHeap.add(maxHeap.poll());
    if (maxHeap.size() < minHeap.size()) {
      maxHeap.add(minHeap.poll());
    }
  };

  median = () => {
    if (maxHeap.size() > minHeap.size()) {
      return maxHeap.peek();
    }
    return (minHeap.peek() + maxHeap.peek()) / 2;
  };
}

Demo

Java

class MedianFinder {
 public PriorityQueue < Integer > maxHeap;
 public PriorityQueue < Integer > minHeap;

 /** initialize your data structure here. */
 public MedianFinder() {
  this.maxHeap = new PriorityQueue < > (Collections.reverseOrder());
  this.minHeap = new PriorityQueue < > ();
 }

 public void addNum(int num) {
  this.maxHeap.add(num);
  this.minHeap.add(this.maxHeap.remove());
  if (this.maxHeap.size() < this.minHeap.size()) {
   this.maxHeap.add(this.minHeap.remove());
  }
 }

 public double findMedian() {
  return this.maxHeap.size() > this.minHeap.size() ? this.maxHeap.peek() * 1.0 : (this.maxHeap.peek() + this.minHeap.peek()) * 0.5;
 }
}

/**
 * Your MedianFinder object will be instantiated and called as such:
 * MedianFinder obj = new MedianFinder();
 * obj.addNum(num);
 * double param_2 = obj.findMedian();
 */

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