2021-01-29 973. K Closest Points to Origin

973. K Closest Points to Origin

Difficulty: Medium

Related Topics: Divide and Conquer, Heap, Sort

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. 1 <= K <= points.length <= 10000
2. -10000 < points[i][0] < 10000
3. -10000 < points[i][1] < 10000

Solution

Language: Java

Key: Another way to use divide and conquer to reach only O(n) time complexity

class Solution {
    public int[][] kClosest(int[][] points, int K) {
        List<Point> result = new ArrayList<>();
        int[][] res = new int[K][2];
        Comparator<Point> comp = new Comparator<>() {
            public int compare(Point a, Point b) {
                return a.distance() - b.distance();
            }
        };
        for (int i = 0; i < points.length; i ++) {
            result.add(new Point(points[i][0], points[i][1]));
        }
        Collections.sort(result, comp);
        for (int i = 0; i < K; i++) {
            res[i][0] = result.get(i).x;
            res[i][1] =result.get(i).y;
        }
        return res;
    }
    
}
​
class Point {
    int x;
    int y;
    
    Point(int x, int y) {
        this.x = x;
        this.y = y;
    }
    
    public int distance() {
        return (x * x + y * y);
    }
}