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4d47's solution

to Raindrops in the Crystal Track

Instructions
Test suite
Solution

Convert a number to a string, the contents of which depend on the number's factors.

  • If the number has 3 as a factor, output 'Pling'.
  • If the number has 5 as a factor, output 'Plang'.
  • If the number has 7 as a factor, output 'Plong'.
  • If the number does not have 3, 5, or 7 as a factor, just pass the number's digits straight through.

Examples

  • 28's factors are 1, 2, 4, 7, 14, 28.
    • In raindrop-speak, this would be a simple "Plong".
  • 30's factors are 1, 2, 3, 5, 6, 10, 15, 30.
    • In raindrop-speak, this would be a "PlingPlang".
  • 34 has four factors: 1, 2, 17, and 34.
    • In raindrop-speak, this would be "34".

Setup

Follow the setup instructions for Crystal here:

http://exercism.io/languages/crystal

More help installing can be found here:

http://crystal-lang.org/docs/installation/index.html

Making the Test Suit Pass

Execute the tests with:

$ crystal spec

In each test suite all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by changing pending to it.

Source

A variation on a famous interview question intended to weed out potential candidates. http://jumpstartlab.com

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

raindrops_spec.cr

require "spec"
require "../src/*"

describe "Raindrops" do
  describe "#drops" do
    it "converts 1 to 1" do
      Raindrops.drops(1).should eq "1"
    end

    pending "converts 3 to Pling" do
      Raindrops.drops(3).should eq "Pling"
    end

    pending "converts 5 to Plang" do
      Raindrops.drops(5).should eq "Plang"
    end

    pending "converts 7 to Plong" do
      Raindrops.drops(7).should eq "Plong"
    end

    pending "converts 35 to PlangPlong" do
      Raindrops.drops(35).should eq "PlangPlong"
    end

    pending "converts 52 to 52" do
      Raindrops.drops(52).should eq "52"
    end

    pending "converts 105 to PlingPlangPlong" do
      Raindrops.drops(105).should eq "PlingPlangPlong"
    end
  end
end
class Raindrops
  @@factors = {
    3 => "Pling",
    5 => "Plang",
    7 => "Plong",
  }

  def self.drops(n : Int) : String
    result = @@factors.select { |k| n.divisible_by?(k) }
    result.empty? ? n.to_s : result.values.join
  end
end

What can you learn from this solution?

A huge amount can be learnt from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that I could read more about to develop my understanding?