612. k closest points

 * Definition for a point.
 * class Point {
 *     int x;
 *     int y;
 *     Point() { x = 0; y = 0; }
 *     Point(int a, int b) { x = a; y = b; }
 * } * Definition for a point.
 * class Point {
 *     int x;
 *     int y;
 *     Point() { x = 0; y = 0; }
 *     Point(int a, int b) { x = a; y = b; }
 * }
 */

public class  {
    
     * @param points: a list of points
     * @param origin: a point
     * @param k: An integer
     * @return: the k closest points
     */
    public Point[] kClosest(Point[] points, Point origin, int k) {
        // write your code here
        // max heap
        PriorityQueue<Point> pq = new PriorityQueue<Point>(k, new Comparator<Point>() {
            public int compare(Point a, Point b) {
                int diff = getDistance(b, origin) - getDistance(a, origin);
                if (diff == 0) {
                    diff = b.x - a.x;
                }
                if (diff == 0) {
                    diff = b.y - a.y;
                }
                return diff;

            }

        }
            );
            Point[] result = new Point[k];

            for (int i = 0; i < points.length; i++) {
                pq.offer(points[i]);
                if (pq.size() > k) {
                    pq.poll();
                }
            }
            while (!pq.isEmpty()) {
                result[--k] = pq.poll(); // 先减 --k！！！
            }
            return result;

    }
    private int getDistance(Point a, Point b) {
        return (a.x - b.x)*(a.x - b.x) + (a.y - b.y)*(a.y - b.y);
    }
}