解题思路：

小顶堆 + 大顶堆

class MedianFinder {Queue<Integer> A, B;public MedianFinder() {A = new PriorityQueue<>();B = new PriorityQueue<>((x, y) -> (y - x));}public void addNum(int num) {if (A.size() != B.size()) {A.add(num);B.add(A.poll());} else {B.add(num);A.add(B.poll());}}public double findMedian() {return A.size() != B.size() ? A.peek() : (A.peek() + B.peek()) / 2.0;}
}