思路

code

import java.util.PriorityQueue;
class MedianFinder {
    private int count;
    private PriorityQueue<Integer> maxheap;
    private PriorityQueue<Integer> minheap;
    /** initialize your data structure here. */
    public MedianFinder() {
        count = 0;
        maxheap = new PriorityQueue<>((x,y)->y-x);//使用lambda来声明一个大根堆
        minheap = new PriorityQueue<>();
    }
    public void addNum(int num) {
        count++;
        maxheap.offer(num);  //数据先流入左半部分的大根堆
        minheap.add(maxheap.poll());  //大根堆顶部流入右半部分的小根堆
        if((count&1)!=0)     //如果是偶数 将右半部分的最小元素流入左根堆
            maxheap.add(minheap.poll());
    }
    public double findMedian() {
        if(count&1==0)
            return (double)maxheap.peek()+minheap.peek()/2;
        else
            return (double)maxheap.peek();
    }
}