WeightSorting.scala

import scala.annotation.tailrec
import scala.collection.immutable.ListMap

object WeightSorting extends App {

  def sortWeight(str: String): String = {
    val map = str
      .split(" ") //split by empty space
      .map(s => (sumTailRecursive(s), s)) //let's create a tuple of (weight, string)
      .groupBy(_._1) //group it by weight
      .mapValues(s => s.map(_._2).sorted.mkString(" ")) //convert the values to a list, sort it by string

    //sort the current map in a new one, take the values and return a string
    ListMap(map.toSeq.sortBy(_._1): _*).values.mkString(" ")
  }

  def sumTailRecursive(s: String): Long = {
    val init = s.toLong
    @tailrec
    def go(value: Long, acc: Long): Long = {
      if (value == 0) acc else {
        val lastDigit = value % 10
        val headTail = value / 10
        go(headTail, acc + lastDigit)
      }
    }
    go(init, 0)
  }
  
  def sumRecursive(digit: Long): Long = {
    if (digit == 0) 0
    else digit % 10 + sumRecursive(digit / 10)
  }

  //2000 103 123 4444 99
  println(sortWeight("103 123 4444 99 2000"))

  //11 11 2000 10003 22 123 1234000 44444444 9999
  println(sortWeight("2000 10003 1234000 44444444 9999 11 11 22 123"))
}