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paulfioravanti's solution

to Resistor Color Duo in the Ruby Track

Published at May 07 2019 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

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 acts as a digit of a number. 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 two colors as input, and output the correct number.

The band colors are encoded as follows:

  • Black: 0
  • Brown: 1
  • Red: 2
  • Orange: 3
  • Yellow: 4
  • Green: 5
  • Blue: 6
  • Violet: 7
  • Grey: 8
  • White: 9

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

Source

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.

resistor_color_duo_test.rb

require 'minitest/autorun'
require_relative 'resistor_color_duo'

# Common test data version: 2.0.0 8b44ce1
class ResistorColorDuoTest < Minitest::Test
  def test_brown_and_black
    # skip
    assert_equal 10, ResistorColorDuo.value(["brown", "black"])
  end

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

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

  def test_orange_and_orange
    skip
    assert_equal 33, ResistorColorDuo.value(["orange", "orange"])
  end
end
# frozen_string_literal: true

module ResistorColorDuo
  RESISTOR_VALUES = {
    "black" => "0",
    "brown" => "1",
    "red" => "2",
    "orange" => "3",
    "yellow" => "4",
    "green" => "5",
    "blue" => "6",
    "violet" => "7",
    "grey" => "8",
    "white" => "9"
  }.freeze
  private_constant :RESISTOR_VALUES

  module_function

  def value(bands)
    bands
      .reduce("", &method(:add_resistor_value))
      .to_i
  end

  def add_resistor_value(acc, band)
    acc + RESISTOR_VALUES[band]
  end
  private_class_method :add_resistor_value
end

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