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@Yano 2019-01-13T07:33:01.000000Z 字数 1548 阅读 1043

LeetCode 973 K Closest Points to Origin

LeetCode


题目描述

We have a list of points on the plane. Find the K closest points to the origin (0, 0).

(Here, the distance between two points on a plane is the Euclidean distance.)

You may return the answer in any order. The answer is guaranteed to be unique (except for the order that it is in.)

Example 1:

Input: points = [[1,3],[-2,2]], K = 1
Output: [[-2,2]]
Explanation: 
The distance between (1, 3) and the origin is sqrt(10).
The distance between (-2, 2) and the origin is sqrt(8).
Since sqrt(8) < sqrt(10), (-2, 2) is closer to the origin.
We only want the closest K = 1 points from the origin, so the answer is just [[-2,2]].

Example 2:

Input: points = [[3,3],[5,-1],[-2,4]], K = 2
Output: [[3,3],[-2,4]]
(The answer [[-2,4],[3,3]] would also be accepted.)

Note:

1 <= K <= points.length <= 10000
-10000 < points[i][0] < 10000
-10000 < points[i][1] < 10000

代码

想到的最直接的方法,就是根据坐标的平方和排序,用一个map记录结果,key为每个点的平方和,value是结果为key的一组点。

  1. public int[][] kClosest(int[][] points, int K) {
  2. if (points.length < K) return null;
  3. int[][] ans = new int[K][2];
  4. Map<Long, List<Point>> map = new HashMap<>();
  5. List<Long> sort = new ArrayList<>();
  6. for (int[] point : points) {
  7. long d = point[0] * point[0] + point[1] * point[1];
  8. if (map.containsKey(d)) {
  9. map.get(d).add(new Point(point));
  10. } else {
  11. ArrayList<Point> list = new ArrayList<Point>();
  12. list.add(new Point(point));
  13. map.put(d, list);
  14. sort.add(d);
  15. }
  16. }
  17. Collections.sort(sort);
  18. int count = 0, i = 0;
  19. while (count < K) {
  20. long d = sort.get(i++);
  21. List<Point> tmp = map.get(d);
  22. for (int i1 = 0; i1 < tmp.size(); i1++) {
  23. ans[count++] = new int[]{tmp.get(i1).getX(), tmp.get(i1).getY()};
  24. }
  25. }
  26. return ans;
  27. }
  28. private static class Point {
  29. private int x;
  30. private int y;
  31. public Point(int[] p) {
  32. this.x = p[0];
  33. this.y = p[1];
  34. }
  35. public int getX() {
  36. return x;
  37. }
  38. public int getY() {
  39. return y;
  40. }
  41. }
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