Tuesday, August 12, 2014

Scalarific FizzBuzz

This started as a lunchtime conversation about interviewing. I'm a big fan of FizzBuzz as a “screening” question: it weeds out the people that shouldn't be allowed near a computer (and, after conducting several hundred interviews, I can say that there's a depressingly large number of them, especially at a company without a preliminary phone screen).

For a Scala developer, what constitutes a good FizzBuzz? Clearly, it should be based around higher-order functions, such as a map() (and, as I don't consider myself a Scala developer, I'll leave the parentheses and dots in place):

(1 to 20).map(???)

A simple implementation might use an if expression:

def fbi(x: Int): String = {
    if ((x % 15) == 0) "fizzbuzz"
    else if ((x % 3) == 0) "fizz"
    else if ((x % 5) == 0) "buzz"
    else s"$x"

It gets the job done, but looks too much like Java. We need to add some Scala-specific syntax:

def fbm(x: Int): String = x match {
    case n if ((n % 15) == 0) => "fizzbuzz"
    case n if ((n % 3) == 0) => "fizz"
    case n if ((n % 5) == 0) => "buzz"
    case n => s"$n"

You can argue whether this is better or worse. It seems to me that it just wraps the previous if with more cruft.* As our conversation devolved, though, it led to the following implementation, which is about as far from Java as I can imagine:

object Fizz {
    def unapply(x: Int): Boolean = ((x % 3) == 0)
object Buzz {
    def unapply(x: Int): Boolean = ((x % 5) == 0)
object FizzBuzz {
    def unapply(x: Int): Boolean = ((x % 15) == 0)
def fbme(x: Int): String = x match {
    case FizzBuzz() => "fizzbuzz"
    case Fizz() => "fizz"
    case Buzz() => "buzz"
    case n => s"$n"

Mind you, I don't think I'd want to hire someone who implemented FizzBuzz this way.

* You'll find a nicer match-based implementation at RosettaCode. Along with some versions that make my extractor-based implementation look sane.