leetcode:295. Find Median from Data Stream

Median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value. So the median is the mean of the two middle value.

Examples:
[2,3,4] , the median is 3

[2,3], the median is (2 + 3) / 2 = 2.5

Design a data structure that supports the following two operations:

void addNum(int num) - Add a integer number from the data stream to the data structure.
double findMedian() - Return the median of all elements so far.
For example:

add(1)
add(2)
findMedian() -> 1.5
add(3)
findMedian() -> 2

给出一串数字流水，要求求出他的中位数
中位数就是一串已排序数组中中间位置的数字，偶数长度取和除2，
所以使用两个队列，一个保存前半段的队列，一个保存后半段的队列，
保存前半段的是极大堆，保存后半段的是极小堆，每次取堆顶元素可以保证就是中位数

import java.util.Comparator;import java.util.PriorityQueue;public class MedianFinder {    // Adds a number into the data structure.    PriorityQueue<Long> maxHeap = new PriorityQueue<>(new Comparator<Long>() {        public int compare(Long o1, Long o2) {            long o = o2 - o1;            return (int) o;        }    });    PriorityQueue<Long> minHeap = new PriorityQueue<>(new Comparator<Long>() {        public int compare(Long o1, Long o2) {            long o = o1 - o2;            return (int) o;        }    });    public void addNum(int num) {        maxHeap.add(num + 0L);        minHeap.add(maxHeap.poll());        if(minHeap.size() - maxHeap.size() > 1){            maxHeap.add(minHeap.poll());        }    }    // Returns the median of current data stream    public double findMedian() {        return minHeap.size() > maxHeap.size() ? minHeap.peek() : (minHeap.peek() + maxHeap.peek()) / 2.0;    }    public static void main(String[] args) {        PriorityQueue<Integer> q = new PriorityQueue<>(new Comparator<Integer>() {            public int compare(Integer o1, Integer o2) {                int o = o1 - o2;                return o;            }        });        q.add(1);        q.add(2);        q.add(3);        System.out.println(q.poll());        MedianFinder m = new MedianFinder();        m.addNum(1);        System.out.println(m.findMedian());        m.addNum(2);        System.out.println(m.findMedian());        m.addNum(3);        System.out.println(m.findMedian());        m.addNum(-4);        System.out.println(m.findMedian());        m.addNum(-5);        System.out.println(m.findMedian());    }};// Your MedianFinder object will be instantiated and called as such:// MedianFinder mf = new MedianFinder();// mf.addNum(1);// mf.findMedian();