[LC] 973. K Closest Points to Origin

Posted 2021-03-02 xuanlu

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.)

 

class Solution {
    public int[][] kClosest(int[][] points, int K) {
        // keep max heap
        PriorityQueue<Cell> pq = new PriorityQueue<>((a, b) -> (b.x)*(b.x)+ (b.y)*(b.y) - (a.x)*(a.x) - (a.y)*(a.y));

        for (int[] point: points) {
            pq.offer(new Cell(point[0], point[1]));
            if (pq.size() > K) {
                pq.poll();
            }
        }
        int[][] res = new int[K][2];
        for (int i = K - 1; i >= 0; i--) {
            Cell cur = pq.poll();
            res[i][0] = cur.x;
            res[i][1] = cur.y;
        }
        return res;
    }
}

class Cell {
    int x;
    int y;
    public Cell(int x, int y) {
        this.x = x;
        this.y = y;
    }
}