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to Secret Handshake in the Ruby Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

There are 10 types of people in the world: Those who understand binary, and those who don't.

You and your fellow cohort of those in the "know" when it comes to binary decide to come up with a secret "handshake".

1 = wink
10 = double blink
100 = close your eyes
1000 = jump


10000 = Reverse the order of the operations in the secret handshake.

Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.

Here's a couple of examples:

Given the input 3, the function would return the array ["wink", "double blink"] because 3 is 11 in binary.

Given the input 19, the function would return the array ["double blink", "wink"] because 19 is 10011 in binary. Notice that the addition of 16 (10000 in binary) has caused the array to be reversed.


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 secret_handshake_test.rb

To include color from the command line:

ruby -r minitest/pride secret_handshake_test.rb

Source

Bert, in Mary Poppins http://www.imdb.com/title/tt0058331/quotes/qt0437047

Submitting Incomplete Solutions

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

secret_handshake_test.rb

require 'minitest/autorun'
require_relative 'secret_handshake'

class SecretHandshakeTest < Minitest::Test
  def test_handshake_1_to_wink
    handshake = SecretHandshake.new(1)
    assert_equal ['wink'], handshake.commands
  end

  def test_handshake_10_to_double_blink
    skip
    handshake = SecretHandshake.new(2)
    assert_equal ['double blink'], handshake.commands
  end

  def test_handshake_100_to_close_your_eyes
    skip
    handshake = SecretHandshake.new(4)
    assert_equal ['close your eyes'], handshake.commands
  end

  def test_handshake_1000_to_jump
    skip
    handshake = SecretHandshake.new(8)
    assert_equal ['jump'], handshake.commands
  end

  def test_handshake_11_to_wink_and_double_blink
    skip
    handshake = SecretHandshake.new(3)
    assert_equal ['wink', 'double blink'], handshake.commands
  end

  def test_handshake_10011_to_double_blink_and_wink
    skip
    handshake = SecretHandshake.new(19)
    assert_equal ['double blink', 'wink'], handshake.commands
  end

  def test_handshake_11111_to_double_blink_and_wink
    skip
    handshake = SecretHandshake.new(31)
    expected = ['jump', 'close your eyes', 'double blink', 'wink']
    assert_equal expected, handshake.commands
  end

  def test_invalid_handshake
    skip
    handshake = SecretHandshake.new('piggies')
    assert_equal [], handshake.commands
  end
end
# frozen_string_literal: true

class SecretHandshake
  ACTIONS = [
    [:<<, "wink"],
    [:<<, "double blink"],
    [:<<, "close your eyes"],
    [:<<, "jump"],
    [:reverse!]
  ].freeze
  private_constant :ACTIONS
  NUMBER = /\A\d+\z/.freeze
  private_constant :NUMBER
  MASK = ->(number) { 1 << number }
  private_constant :MASK

  def initialize(number)
    @number = number
  end

  def commands
    return [] unless number.to_s.match?(NUMBER)

    ACTIONS
      .each
      .with_index
      .with_object([], &method(:perform_secret_handshake))
  end

  private

  def perform_secret_handshake((action, index), acc)
    acc.public_send(*action) if set?(index)
  end

  def set?(index)
    (number & MASK[index]).positive?
  end

  attr_reader :number
end

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