General FizzBuzz in Scala

Question

I wanted to create a FizzBuzz implementation that both showcases the strengths of Scala (Functional paradigm and collections) and is general enough to anticipate the typical interview follow-up questions. i.e. What if fizz was for factors of 4 instead? What if we wanted to replace factors of 7 with "foo"?

object FizzBuzz extends App {

  def fizzbuzz(factors: Map[Int, String])(currentNumber: Int): String = {
    val words = factors.filter(currentNumber % _._1 == 0).values
    if (words.isEmpty) currentNumber.toString else words.mkString("")
  }

  private final val Factors = Map(3 -> "fizz", 5 -> "buzz")
  private final val Range = 1 to 100

  Range.map(fizzbuzz(Factors)).foreach(println)
}

I would appreciate any feedback on how I can make my Scala more idiomatic.

Answer 1

Map is not guaranteed to impose or preserve any order for its entries. For example, if I change Factors to …

private final val Factors = Map(3 -> "a", 5 -> "b", 6 -> "c", 7 -> "d", 8 -> "e", 9 -> "f")

… I get:

⁞
89
bcfa
d
92
a
94
b
cae
97
d
fa
b

So, the fact that you get "fizzbuzz" rather than "buzzfizz" is based on luck, not skill. If you want to guarantee "fizzbuzz", you need a scala.collection.immutable.SortedMap.

Answer 2

Because you want to be able to change the mapping of fizz and buzz I would think to make a funcion that take a function as an argument that maps a number to a string:

def fizzbuzz(countUntil: Int)(mapping: Int => String) = {
  for (i <- 0 to countUntil) yield mapping(i)
}

Then you can call the function like this:

// Map Int to String using pattern matching with a guard
fizzbuzz(30) {
  case fizzbuzz if fizzbuzz % 3 == 0 && fizzbuzz % 5 == 0 => "fizzbuzz"
  case fizz if fizz % 3 == 0 => "fizz"
  case buzz if buzz % 5 == 0 => "buzz"
  case f => s"$f"
}.foreach(println)

The pattern matching code could be an if/else just as long as it takes an Int and returns a String for example:

// Map Int to String using if/else
fizzbuzz(30){ f =>
  if (f % 3 == 0 && f % 5 == 0) "fizzbuzz"
  else if (f % 3 == 0) "fizz"
  else if (f % 5 == 0) "buzz"
  else s"$f"
}.foreach(println)