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:
For example:
add(1) add(2) findMedian() -> 1.5 add(3) findMedian() -> 2
public class MedianFinder { int count = 0; int median = 0; PriorityQueue<Integer> q1 = new PriorityQueue<Integer>(new Comparator<Integer>(){ public int compare(Integer a, Integer b){ return b-a; } }); PriorityQueue<Integer> q2 = new PriorityQueue<Integer>(); // Adds a number into the data structure. public void addNum(int num) { count++; q1.add(num); q2.add(q1.poll()); if(q1.size() < q2.size()) q1.add(q2.poll()); } // Returns the median of current data stream public double findMedian() { if(count > 0 && count % 2 == 0) return ((double)(q1.peek()) + (double)(q2.peek()))/2.0; else return q1.peek(); } }; // Your MedianFinder object will be instantiated and called as such: // MedianFinder mf = new MedianFinder(); // mf.addNum(1); // mf.findMedian();
295. Find Median from Data Stream
原文：http://www.cnblogs.com/joannacode/p/6132575.html