trjhtr

For my first attempt at Scala I decided to solve a simple exercise on codingame.com.

Based on a string input containing the user location, the defibrillators count and a list of defibrillators entries (id, name, address, phone number, longitude, latitude), I have to print the closest defibrillator from the user. The distance formula is given in the rules.

An example of input:

3,879483
43,608177
3
1;Maison de la Prevention Sante;6 rue Maguelone 340000 Montpellier;;3,87952263361082;43,6071285339217
2;Hotel de Ville;1 place Georges Freche 34267 Montpellier;;3,89652239197876;43,5987299452849
3;Zoo de Lunaret;50 avenue Agropolis 34090 Mtp;;3,87388031141133;43,6395872778854

import math._
import scala.util._

object Solution extends App 
 val playerLongitude = readLine
 val playerLatitude = readLine
 val defibrilatorCount = readInt

 def sanitizeString(string : String) : String = string.replace(',', '.')
 def stringToDouble(string : String) : Double = sanitizeString(string).toDouble

 val playerLongitudeValue = stringToDouble(playerLongitude)
 val playerLatitudeValue = stringToDouble(playerLatitude)

 def distanceToPlayer(long : Double, lat : Double) : Double = 
 val x = (long - playerLongitudeValue) * cos((playerLatitudeValue + lat) / 2)
 val y = lat - playerLatitudeValue
 sqrt(x * x + y * y) * 6371;
 

 def distanceToPlayer(stringInput : String) : Double = 
 val tokens = sanitizeString(stringInput).split(";")
 distanceToPlayer(tokens(4).toDouble, tokens(5).toDouble)
 

 var smallestDistance = Double.MaxValue
 var closestDefibName = ""

 for(i <- 0 until defibrilatorCount) 
 val defib = readLine
 val distance = distanceToPlayer(defib)
 if(distance < smallestDistance) 
 smallestDistance = distance
 closestDefibName = defib.split(";")(1)
 
 

 println(closestDefibName)

The main observation I would make is that this code — particularly the for loop — looks very procedural. To find the minimum of some collection as determined by some metric, use .minBy[B](f: (A) ⇒ B): A.

For readability, avoid interleaving function definitions with the execution flow. Put all of the definitions first, if possible.

You potentially split each defibrillator input line twice: once to extract the coordinates, then maybe again if you are interested in extracting the name. I suggest parsing each line once and constructing a case class object from it.

Your sanitizeString function is rather heavy-handed. To parse French-formatted decimals, use java.text.NumberFormat.

Note that defibrilatorCount is misspelled.

Suggested solution

import math.cos, sqrt
import io.StdIn.readInt, readLine
import java.text.NumberFormat
import java.util.Locale

object Solution extends App 
 val frenchFmt = NumberFormat.getInstance(Locale.FRANCE)
 def parseDouble(s: String): Double = frenchFmt.parse(s).doubleValue

 case class GeoObject(long: Double, lat: Double, name: String)

 def parseDefibrillator(line: String): GeoObject = 
 val fields = line.split(";")
 GeoObject(parseDouble(fields(4)), parseDouble(fields(5)), fields(1))
 

 def distanceMetric(a: GeoObject, b: GeoObject): Double = 
 val x = (a.long - b.long) * cos((a.lat + a.lat) / 2)
 val y = a.lat - b.lat
 6371 * sqrt(x * x + y * y)
 // Note: 6371 * sqrt is optional, if just comparing distances
 

 val player = GeoObject(parseDouble(readLine), parseDouble(readLine), null)
 val count = readInt
 val nearest = (0 until count).map(_ => parseDefibrillator(readLine))
 .minBy(distanceMetric(player, _))
 println(nearest.name)