Exercism v3 launches on Sept 1st 2021. Learn more! ๐Ÿš€๐Ÿš€๐Ÿš€
Avatar of PatrickMcSweeny

PatrickMcSweeny's solution

to Resistor Color Duo in the Ruby Track

Published at Aug 21 2019 · 0 comments
Test suite

If you want to build something using a Raspberry Pi, you'll probably use resistors. For this exercise, you need to know two things about them:

  • Each resistor has a resistance value.
  • Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read. To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values. Each band has a position and a numeric value. For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.

In this exercise you are going to create a helpful program so that you don't have to remember the values of the bands. The program will take color names as input and output a two digit number, even if the input is more than two colors!

The colors are mapped to the numbers from 0 to 9 in the sequence: Black - Brown - Red - Orange - Yellow - Green - Blue - Violet - Grey - White

From the example above: brown-green should return 15 brown-green-violet should return 15 too, ignoring the third color.

For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby resistor_color_duo_test.rb

To include color from the command line:

ruby -r minitest/pride resistor_color_duo_test.rb


Maud de Vries, Erik Schierboom https://github.com/exercism/problem-specifications/issues/1464

Submitting Incomplete Solutions

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


require 'minitest/autorun'
require_relative 'resistor_color_duo'

# Common test data version: 2.1.0 00dda3a
class ResistorColorDuoTest < Minitest::Test
  def test_brown_and_black
    # skip
    assert_equal 10, ResistorColorDuo.value(["brown", "black"])

  def test_blue_and_grey
    assert_equal 68, ResistorColorDuo.value(["blue", "grey"])

  def test_yellow_and_violet
    assert_equal 47, ResistorColorDuo.value(["yellow", "violet"])

  def test_orange_and_orange
    assert_equal 33, ResistorColorDuo.value(["orange", "orange"])

  def test_ignore_additional_colors
    assert_equal 51, ResistorColorDuo.value(["green", "brown", "orange"])
COLORS = %w[black brown red orange yellow green blue violet grey white].freeze

class ResistorColorDuo
  def self.value(colors)
    colors.first(2).map { |color| COLORS.find_index color }.join('').to_i

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other peopleโ€™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 you could read more about to improve your understanding?