Feature #1: Select Closest Drivers

Sumit Rawal answered on May 24, 2023 Popularity 1/10 Helpfulness 1/10

answer Feature #1: Select Closest Drivers

Feature #1: Select Closest Drivers

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Solution

The Euclidean distance between a point P(x,y) and the origin can be calculated using the following formula:

Now that you can calculate the distance between a user and all nearby drivers, how will you find the K nearest drivers? The best data structure that comes to mind to track the nearest K drivers is Heap.

We iterate through the array and calculate the distance between each driver’s current location and the user. We’ll insert the distances of the first K drivers into the Heap. Each time we find a distance smaller than the maximum distance in the Heap, we do two things:

Remove the maximum distance from the Heap

Insert the smaller distance into the Heap

This will ensure that we always have K minimum distances in the Heap. The most efficient way to repeatedly find the maximum number among a set of numbers is to use a max-Heap.

Below is an illustration of this process. We have mapped the city of Seattle onto the cartesian plane to get simpler latitude and longitude values for the driver’s location.

import scala.collection.mutable.PriorityQueue
import scala.collection.immutable.List
class Location(var x: Int, var y: Int) {
  def distFromOrigin: Int = { // ignoring sqrt
    (x * x) + (y * y)
  }
}

object Main {
  def findClosestDrivers(locations: Array[Location], k: Int): List[Location] = {
    val maxHeap = new PriorityQueue[Location]()((p1:Location,p2:Location) => p1.distFromOrigin - p2.distFromOrigin)
    // put first 'k' locations in the max heap
    for (i <- 0 until k) {
      maxHeap += locations(i)
    }
    // go through the remaining locations of the input array, if a Location is closer to the origin than the top Location
    // of the max-heap, remove the top Location from heap and add the Location from the input array
    for (i <- k until locations.length) {
      if (locations(i).distFromOrigin < maxHeap.head.distFromOrigin) {
        maxHeap.dequeue()
        maxHeap += locations(i)
      }
    }
    // the heap has 'k' locations closest to the origin, return them in a list
    maxHeap.toList
  }

  def main(args: Array[String]): Unit = {
    val locations = Array[Location](new Location(1, 3), new Location(3, 4), new Location(2, -1))
    val result = findClosestDrivers(locations, 2)
    System.out.print("Here are the k drivers locations closest to the user in the Seattle area: ")

    for (p <- result) {
      System.out.print("[" + p.x + " , " + p.y + "] ")
    }
  }
}

Popularity 1/10 Helpfulness 1/10 Language scala

Source: Grepper

Tags: closest drivers scala select

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Contributed on May 24 2023

Sumit Rawal

0 Answers Avg Quality 2/10

Feature #1: Select Closest Drivers

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