k-closest-points（K个最接近的点 ）PriorityQueue

描述

给定一些 points 和一个 origin，从 points 中找到 k 个离 origin 最近的点。按照距离由小到大返回。如果两个点有相同距离，则按照x值来排序；若x值也相同，就再按照y值排序。

心得

复习了comparator的重写，与Arrays.sort()差不多，重写comparator的compare函数，可以实现自定义排序。升序前减后，降序后减前。

代码

 * class Point {
 *     int x;
 *     int y;
 *     Point() { x = 0; y = 0; }
 *     Point(int a, int b) { x = a; y = b; }
 * }
 */
class Pair {
    int x,y,d;
    Pair(int x, int y, int d) {
        this.x = x;
        this.y = y;
        this.d = d;
    }
}

public class Solution {
    /**
     * @param points: a list of points
     * @param origin: a point
     * @param k: An integer
     * @return: the k closest points
     */
    public int distance(Point point, Point origin) {
        int x = point.x - origin.x;
        int y = point.y - origin.y;
        int result = x*x+y*y;
        return result;
    }
    public Point[] kClosest(Point[] points, Point origin, int k) {
        // write your code here
        Pair[] p = new Pair[points.length];
        Point[] result5 = new Point[k];
        for(int i = 0; i < points.length;i++) {
            Pair tmp9 = new Pair(points[i].x,points[i].y,distance(points[i], origin));
            p[i] = tmp9;
        }
        PriorityQueue queue = new PriorityQueue(k,new Comparator(){  
            @Override    //重写compare函数
            public int compare(Pair a, Pair b) {
                if(a.d == b.d) {
                    if(a.x == b.x) {
                        return a.y - b.y;
                    }
                    else {
                        return a.x - b.x;
                    }
                }
                else {
                    return a.d - b.d;
                }
            }
        });
        
        for(int i =0; i < p.length; i++) {
            queue.offer(p[i]);
        }
        for(int i = 0; i < k;i++) {
            Pair tmp = queue.poll();
            Point tmp2 = new Point(tmp.x,tmp.y);
            result5[i] = tmp2;
        }
        return result5;
    }
}