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Avatar of stevensonmt

stevensonmt's solution

to Raindrops in the Crystal Track

Published at Jul 13 2018 · 1 comment
Instructions
Test suite
Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

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
  def self.drops(number)
    String.build do |output|
      factors = { 3 => "Pling", 5 => "Plang", 7 => "Plong" }
      factors.each do |factor, value|
        case {number % factor}
        when { 0 }
          output << value
        end
      end
      output  << number.to_s if output.empty?
    end

  end
end

Community comments

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Avatar of jedschneider

I would pull factors out into a constant or a configurable data value. It doesn't belong inside the method doing the work. Otherwise, I like using String.build as you did. Nice job.

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