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May Leetcode Challenge - Day 30

K Closest Points to Origin

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

Solution

It's similar to find K largest (or smallest) elements in array.

Lazy way: Sort then pick first K elements, O(nlogn + k).
Optimized way: Use Heap, O(n + klogn), n for build heap, klogn for finding first K elements.

Details

class Solution {
    func kClosest(_ points: [[Int]], _ K: Int) -> [[Int]] {
        let sorted = points.map { Point($0) } .sorted(by: <)
        return sorted[..<K].map { [$0.x, $0.y] }
    }
    
}

struct Point {
    var x: Int
    var y: Int
    let distance: Int
    init(_ data: [Int]) {
        self.x = data[0]
        self.y = data[1]
        distance = x * x + y * y
    }
}

extension Point: Comparable {
    static func <(lhs: Point, rhs: Point) -> Bool {
        return lhs.distance < rhs.distance
    }
    static func ==(lhs: Point, rhs: Point) -> Bool {
        return lhs.distance == rhs.distance
    }
}

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