LuhnApp.scala

package com.github.modalsoul.luhn

object LuhnApp extends App {
  // Success
  println(Luhn.check("49927398716"))
  // Failure
  println(Luhn.check("49972398716"))
}

object Luhn {
  def check(numbers:String):Boolean = check(numbers.map(_.asDigit))

  def check(numbers:Seq[Int]):Boolean = {
    val sum = numbers.reverse.zipWithIndex.map { case (n, index) =>
      if((index)%2 == 1) n*2 else n
    }.reduce{(z, n) =>
      z + (if(n < 10) n else n%10 + n/10)
    }
    sum%10 == 0
  }
}