Scala algorithm: Fizz Buzz in purely functional immutable Scala

Algorithm goal

FizzBuzz is one of the most general and common programming questions, and tells about programming skills the most. It is ubiquitous.

It challenges notions of how to deal with combining output types, working in terms of expressions versus statements, and also parametrisation versus hard-coding.

This problem is particularly suited for Scala as it permits many different styles of programming - so even if you have the produced the expected result, it does not mean that you have the most idiomatic code. Often, in other programming languages, it is in fact more convenient and effective to write code in a more mutable style.

The problem statement is: for every number, you should be able to output 'Fizz' if it is divisible by 3, 'Buzz', if it is divisible by 5, 'FizzBuzz' if it is divisible by 3 * 5 (so that the words are combined), and in all other cases such as '14', return '14', the original number.

Algorithm in Scala

13 lines of Scala (compatible versions 2.13 & 3.0), showing how concise Scala can be!

val NumToString = List(3 -> "Fizz", 5 -> "Buzz")

def fizzBuzz(n: Int): String = {
  def isDivisibleBy(i: Int): Boolean = n % i == 0
  NumToString.collect({
    case (n, str) if isDivisibleBy(n) => str
  }) match {
    case Nil =>
      s"$n"
    case strings =>
      strings.mkString
  }
}

Test cases in Scala

assert(fizzBuzz(1) == "1")
assert(fizzBuzz(2) == "2")
assert(fizzBuzz(3) == "Fizz")
assert(fizzBuzz(5) == "Buzz")
assert(fizzBuzz(12) == "Fizz")
assert(fizzBuzz(13) == "13")
assert(fizzBuzz(15) == "FizzBuzz")

Explanation

Firstly, we declare a mapping from number to a word. This immediately separates you away from classes of other programmers, who would proceed to hard-code numbers 3 and 5 in the logic of the 'fizzBuzz' function itself.

With Scala's 'collect' method, you can do a 'filter' and a 'map' operation in one go, saving on typing. Here, we collect all the numbers with their corresponding words, and get a List as output. If there are no words that were discovered in the candidate checking process, this means that we must return the original number; otherwise, we return the combination of words (this is © from www.scala-algorithms.com)

Scala concepts & Hints

  1. Collect

    'collect' allows you to use Pattern Matching, to filter and map items.

    assert("Hello World".collect {
      case character if Character.isUpperCase(character) => character.toLower
    } == "hw")
    
  2. Def Inside Def

    A great aspect of Scala is being able to declare functions inside functions, making it possible to reduce repetition.

    def exampleDef(input: String): String = {
      def surroundInputWith(char: Char): String = s"$char$input$char"
      surroundInputWith('-')
    }
    
    assert(exampleDef("test") == "-test-")
    

    It is also frequently used in combination with Tail Recursion.

  3. Pattern Matching

    Pattern matching in Scala lets you quickly identify what you are looking for in a data, and also extract it.

    assert("Hello World".collect {
      case character if Character.isUpperCase(character) => character.toLower
    } == "hw")
    

Scala Algorithms: The most comprehensive library of algorithms in standard pure-functional Scala

Think in Scala & master the highest paid programming language in the US

Scala is used at many places, such as AirBnB, Apple, Bank of America, BBC, Barclays, Capital One, Citibank, Coursera, eBay, JP Morgan, LinkedIn, Morgan Stanley, Netflix, Singapore Exchange, Twitter.

Study our 92 Scala Algorithms: 6 fully free, 74 published & 18 upcoming

Fully unit-tested, with explanations and relevant concepts; new algorithms published about once a week.

  1. Compute the length of longest valid parentheses
  2. Check a binary tree is balanced
  3. Make a queue using stacks (Lists in Scala)
  4. Find height of binary tree
  5. Single-elimination tournament tree
  6. Quick Sort sorting algorithm in pure immutable Scala
  7. Find minimum missing positive number in a sequence
  8. Least-recently used cache (LRU)
  9. Count pairs of a given expected sum
  10. Compute a Roman numeral for an Integer, and vice-versa
  11. Compute keypad possibilities
  12. Matching parentheses algorithm with foldLeft and a state machine
  13. Traverse a tree Breadth-First, immutably
  14. Read a matrix as a spiral
  15. Remove duplicates from a sorted list (state machine)
  16. Merge Sort: stack-safe, tail-recursive, in pure immutable Scala, N-way
  17. Longest increasing sub-sequence length
  18. Reverse first n elements of a queue
  19. Binary search a generic Array
  20. Merge Sort: in pure immutable Scala
  21. Make a queue using Maps
  22. Is an Array a permutation?
  23. Count number of contiguous countries by colors
  24. Add numbers without using addition (plus sign)
  25. Tic Tac Toe MinMax solve
  26. Run-length encoding (RLE) Encoder
  27. Print Alphabet Diamond
  28. Balanced parentheses algorithm with tail-call recursion optimisation
  29. Reverse a String's words efficiently
  30. Count number of changes (manipulations) needed to make an anagram with foldLeft and a MultiSet
  31. Count passing cars
  32. Establish execution order from dependencies
  33. Counting inversions of a sequence (array) using a Merge Sort
  34. Longest common prefix of strings
  35. Check if an array is a palindrome
  36. Check a directed graph has a routing between two nodes (depth-first search)
  37. Compute nth row of Pascal's triangle
  38. Run-length encoding (RLE) Decoder
  39. Check if a number is a palindrome
  40. In a range of numbers, count the numbers divisible by a specific integer
  41. Find the index of a substring ('indexOf')
  42. Reshape a matrix
  43. Compute modulo of an exponent without exponentiation
  44. Closest pair of coordinates in a 2D plane
  45. Find the contiguous slice with the minimum average
  46. Compute maximum sum of subarray (Kadane's algorithm)
  47. Pure-functional double linked list
  48. Binary search in a rotated sorted array
  49. Check if a directed graph has cycles
  50. Rotate Array right in pure-functional Scala - using an unusual immutable efficient approach
  51. Check a binary tree is a search tree
  52. Length of the longest common substring
  53. Tic Tac Toe board check
  54. Find an unpaired number in an array
  55. Check if a String is a palindrome
  56. Count binary gap size of a number using tail recursion
  57. Remove duplicates from a sorted list (Sliding)
  58. Monitor success rate of a process that may fail
  59. Find sub-array with the maximum sum
  60. Find the minimum absolute difference of two partitions
  61. Find maximum potential profit from an array of stock price
  62. Fibonacci in purely functional immutable Scala
  63. Fizz Buzz in purely functional immutable Scala
  64. Find combinations adding up to N (non-unique)
  65. Make a binary search tree (Red-Black tree)
  66. Remove duplicates from an unsorted List
  67. Find combinations adding up to N (unique)
  68. Count factors/divisors of an integer
  69. Compute single-digit sum of digits
  70. Traverse a tree Depth-First
  71. Reverse bits of an integer
  72. Find k closest elements to a value in a sorted Array
  73. QuickSelect Selection Algorithm (kth smallest item/order statistic)
  74. Rotate a matrix by 90 degrees clockwise

Explore the 21 most useful Scala concepts

To save you going through various tutorials, we cherry-picked the most useful Scala concepts in a consistent form.

  1. Class Inside Class
  2. Class Inside Def
  3. Collect
  4. Def Inside Def
  5. Drop, Take, dropRight, takeRight
  6. foldLeft and foldRight
  7. For-comprehension
  8. Lazy List
  9. Option Type
  10. Ordering
  11. Partial Function
  12. Pattern Matching
  13. Range
  14. scanLeft and scanRight
  15. Sliding / Sliding Window
  16. Stack Safety
  17. State machine
  18. Tail Recursion
  19. Type Class
  20. View
  21. Zip

Register now (free)