FB面经 Prepare: K closest point to the origin
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Give n points on 2-D plane, find the K closest points to origin
1 package fbPractise; 2 3 import java.util.*; 4 5 class Coordinate { 6 int x; 7 int y; 8 public Coordinate(int x, int y) { 9 this.x = x; 10 this.y = y; 11 } 12 } 13 14 public class Kclosest { 15 16 public static List<Coordinate> findK(List<Coordinate> input, int k) { 17 HashMap<Coordinate, Integer> map = new HashMap<Coordinate, Integer>(); 18 int longest = 0; 19 for (Coordinate each : input) { 20 int distance = cal(each); 21 map.put(each, distance); 22 longest = Math.max(longest, distance); 23 } 24 25 List<Coordinate>[] arr = new ArrayList[longest + 1]; 26 for (Coordinate each : map.keySet()) { 27 int dis = map.get(each); 28 if (arr[dis] == null) 29 arr[dis] = new ArrayList<Coordinate>(); 30 arr[dis].add(each); 31 } 32 33 List<Coordinate> res = new ArrayList<Coordinate>(); 34 for (int i=0; i<arr.length-1 && res.size()<k; i++) { 35 if (arr[i] != null) 36 res.addAll(arr[i]); 37 } 38 return res; 39 } 40 41 public static int cal(Coordinate a) { 42 return a.x * a.x + a.y * a.y; 43 } 44 45 46 /** 47 * @param args 48 */ 49 public static void main(String[] args) { 50 // TODO Auto-generated method stub 51 Coordinate c1 = new Coordinate(1,2); 52 Coordinate c2 = new Coordinate(1,3); 53 Coordinate c3 = new Coordinate(2,5); 54 List<Coordinate> list = new ArrayList<Coordinate>(); 55 list.add(c1); 56 list.add(c2); 57 list.add(c3); 58 List<Coordinate> res = findK(list, 2); 59 for (Coordinate each : res) { 60 System.out.print(each.x); 61 System.out.println(each.y); 62 } 63 } 64 65 }
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