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murdho's solution

to Raindrops in the Crystal Track

Published at Feb 13 2019 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution 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
  FACTOR_NAMES = {
    3 => "Pling",
    5 => "Plang",
    7 => "Plong",
  }

  def self.drops(n)
    names = FACTOR_NAMES
      .select { |factor, _| n.divisible_by?(factor) }
      .map(&.last)
      .join

    names.empty? ? n.to_s : names
  end
end

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