LeetCode 973. K Closest Points to Origin

原題鏈接在這里：https://leetcode.com/problems/k-closest-points-to-origin/

題目：

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

題解：

用maxHeap來維護K shortest distence.

Time Complexity: O(nlogK). n = points.length.

Space: O(n).

AC Java: 

class Solution {
    public int[][] kClosest(int[][] points, int K) {
        if(points == null || points.length == 0 || K < 1){
            return points;
        }
        
        PriorityQueue<int []> pq = new PriorityQueue<int []>((a, b) -> getDistanceSquare(b)-getDistanceSquare(a));
        for(int [] point : points){
            pq.add(point);
            if(pq.size() > K){
                pq.poll();
            }
        }
        
        int [][] res = new int[K][2];
        for(int i = 0; i<K; i++){
            res[i] = pq.poll();
        }
        
        return res;
    }
    
    private int getDistanceSquare(int [] point){
        return point[0]*point[0] + point[1]*point[1];
    }
}