1 import java.util.Comparator;
 2 import java.util.PriorityQueue;
 3 
 4 
 5 //方法类似与480题的sliding window median
 6  /*
 7      Use two Heaps to store numbers. maxHeap for numbers smaller than current
 8      * median, minHeap for numbers bigger than and equal to current median. A
 9      * small trick I used is always make size of minHeap equal (when there are
10      * even numbers) or 1 element more (when there are odd numbers) than the
11      * size of maxHeap
12     */
13 public class MedianFinder {
14 
15     PriorityQueue<Integer> minHeap;//使minHeap中的个数等于或者比maxHeap多1，这样对于返回中位数操作就相对简单
16     PriorityQueue<Integer> maxHeap;
17 
18     public MedianFinder() {
19         this.minHeap = new PriorityQueue<>();
20         this.maxHeap = new PriorityQueue<>(new Comparator<Integer>() {
21             public int compare(Integer o1, Integer o2) {
22                 return o2.compareTo(o1);
23             }
24         });
25     }
26 
27     public void addNum(int num) {
28         if (num < findMedian())
29             maxHeap.add(num);
30         else
31             minHeap.add(num);
32         if (maxHeap.size() > minHeap.size())
33             minHeap.add(maxHeap.poll());
34         if (minHeap.size() - maxHeap.size() > 1)
35             maxHeap.add(minHeap.poll());
36     }
37 
38     public double findMedian() {
39         if (minHeap.isEmpty() && maxHeap.isEmpty())
40             return 0;
41         if (minHeap.size() == maxHeap.size())
42             return ((double) minHeap.peek() + (double) maxHeap.peek()) / 2.0;
43         else
44             return (double) minHeap.peek();
45     }
46 }