leetcode: Find Median from Data Stream-优快云博客

实际上使用两个队列，保证每个队列顶部恰好是中间的两个值（若large大小大于small，则说明奇数个数字，large的顶部是中间值）...保证这个利用preority queue始终有序的特性...只需保证large的大小永远大于等于small，每次将最小的数给small；而small存数的负数形式（使得顶部最小元素即为实际的最大元素），每次将最大的值给large....这样large中始终存储大得那一半，small中是小的那一半，且二者的顶部最小值恰好是待求得median

class MedianFinder {

    // Adds a number into the data structure.
    Queue<Long> small = new PriorityQueue(),
                large = new PriorityQueue();
    public void addNum(int num) {
        large.add((long)num);
        small.add(-large.poll());
        if( large.size()<small.size() )
        {
            large.add(-small.poll());
        }
    }

    // Returns the median of current data stream
    public double findMedian() {
        if( large.size()>small.size() )
        {
            return large.peek();
        }
        return (double)((large.peek()-small.peek())/2.0);
        
    }
};

// Your MedianFinder object will be instantiated and called as such:
// MedianFinder mf = new MedianFinder();
// mf.addNum(1);
// mf.findMedian();