Exercism: Raindrops

readme.txt

# Raindrops

Write a program that converts a number to a string, the contents of which depends on the number's prime factors.

- If the number contains 3 as a prime factor, output 'Pling'.
- If the number contains 5 as a prime factor, output 'Plang'.
- If the number contains 7 as a prime factor, output 'Plong'.
- If the number does not contain 3, 5, or 7 as a prime factor,
  just pass the number's digits straight through.

## Examples

- 28's prime-factorization is 2, 2, 7.
  - In raindrop-speak, this would be a simple "Plong".
- 1755 prime-factorization is 3, 3, 3, 5, 13.
  - In raindrop-speak, this would be a "PlingPlang".
- The prime factors of 34 are 2 and 17.
  - Raindrop-speak doesn't know what to make of that,
    so it just goes with the straightforward "34".


## Source

A variation on a famous interview question intended to weed out potential candidates. [view source](http://jumpstartlab.com)

raindrops.rb

########## Raindrops Exercism Problem ##############
class Raindrops
  class << self

    def convert(number)
      add_sounds(number) || number.to_s
    end

    private

    FACTOR_STRING_TABLE = {
      3 => 'Pling',
      5 => 'Plang',
      7 => 'Plong'
    }

    def add_sounds(number)
      new_string = ''
      FACTOR_STRING_TABLE.each do |factor, string|
        new_string << string if factor?(number, factor)
      end

      new_string.empty? ? nil : new_string
    end

    def factor?(integer, factor)
      (integer % factor).zero?
    end
  end
end

raindrops_alternate.rb

class Raindrops
  class << self

    def convert(num)
      sounds_for(num) || num.to_s
    end

    private

    def sounds_for(num)
      sounds = ""
      sounds += "Pling" if (num % 3).zero?
      sounds += "Plang" if (num % 5).zero?
      sounds += "Plong" if (num % 7).zero?

      sounds.empty? ? nil : sounds
    end
  end
end

raindrops_test.rb

require 'minitest/autorun'
require_relative 'raindrops'

class RaindropsTest < MiniTest::Unit::TestCase

  def test_1
    assert_equal "1", Raindrops.convert(1)
  end

  def test_3
    assert_equal "Pling", Raindrops.convert(3)
  end

  def test_5
    assert_equal "Plang", Raindrops.convert(5)
  end

  def test_7
    assert_equal "Plong", Raindrops.convert(7)
  end

  def test_6
    assert_equal "Pling", Raindrops.convert(6)
  end

  def test_9
    assert_equal "Pling", Raindrops.convert(9)
  end

  def test_10
    assert_equal "Plang", Raindrops.convert(10)
  end

  def test_14
    assert_equal "Plong", Raindrops.convert(14)
  end

  def test_15
    assert_equal "PlingPlang", Raindrops.convert(15)
  end

  def test_21
    assert_equal "PlingPlong", Raindrops.convert(21)
  end

  def test_25
    assert_equal "Plang", Raindrops.convert(25)
  end

  def test_35
    assert_equal "PlangPlong", Raindrops.convert(35)
  end

  def test_49
    assert_equal "Plong", Raindrops.convert(49)
  end

  def test_52
    skip
    assert_equal "52", Raindrops.convert(52)
  end

  def test_105
    assert_equal "PlingPlangPlong", Raindrops.convert(105)
  end

  def test_12121
    skip
    assert_equal "12121", Raindrops.convert(12121)
  end

end