295. Find Median from Data Stream 295.从数据流中查找中位数

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.

For example,

[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.

 

Example:

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

思路：忘了是怎么最小值都存maxQ，最大值都存minQ的了。原来是：min中存的是max中poll出来的东西

没必要取出来 只是看一看的话，用peek()就行了。poll()是“获取并删除”

class MedianFinder {
    PriorityQueue<Integer> maxQ;
    PriorityQueue<Integer> minQ;

    /** initialize your data structure here. */
    public MedianFinder() {
        maxQ = new PriorityQueue<Integer>();
        //得这么写
        minQ = new PriorityQueue<Integer>(1000, Collections.reverseOrder());
    }
    
    public void addNum(int num) {
        maxQ.offer(num);
        minQ.offer(maxQ.poll());
        
        if (maxQ.size() < minQ.size()) {
            maxQ.offer(minQ.poll());
        }
    }
    
    public double findMedian() {
        if (maxQ.size() == minQ.size()) {
            return (maxQ.peek() + minQ.peek()) / 2.0;
        }else {
            return maxQ.peek();
        }
    }
}

/**
 * Your MedianFinder object will be instantiated and called as such:
 * MedianFinder obj = new MedianFinder();
 * obj.addNum(num);
 * double param_2 = obj.findMedian();
 */