Solution.java

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

    /** initialize your data structure here. */
    public MedianFinder() {
        minHeap = new PriorityQueue<>();
        maxHeap = new PriorityQueue<>(Collections.reverseOrder());
    }
    
    public void addNum(int num) {
        minHeap.offer(num);
        maxHeap.offer(minHeap.poll());
        if (maxHeap.size() - minHeap.size() > 1) {
            minHeap.offer(maxHeap.poll());
        }
    }
    
    public double findMedian() {
        if (maxHeap.size() > minHeap.size()) {
            return maxHeap.peek();
        }
        return (minHeap.peek() + maxHeap.peek()) * 1.0 / 2;
    }
}

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