5、寻找数据流的中位数

/**
 * 设计一个数据结构：
 * 得到一个数据流的中位数
 */
public class MedianFinder {

    PriorityQueue<Integer> bigHeap;
    PriorityQueue<Integer> smallHeap;

    public MedianFinder() {
        bigHeap = new PriorityQueue<>(((o1, o2) -> o2 - o1));
        smallHeap = new PriorityQueue<>();
    }

    public void addNum(int val) {
        bigHeap.add(val);
        smallHeap.add(bigHeap.poll());

        if (bigHeap.size() + 1 < smallHeap.size()) {
            bigHeap.add(smallHeap.poll());
        }
    }

    public double findMedian() {
        if (smallHeap.size() > bigHeap.size())
            return smallHeap.size();

        return (double) (smallHeap.peek() + bigHeap.peek());
    }
}