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PatrickMcSweeny's solution

to Clock in the Ruby Track

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Instructions
Test suite
Solution

Implement a clock that handles times without dates.

You should be able to add and subtract minutes to it.

Two clocks that represent the same time should be equal to each other.


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 clock_test.rb

To include color from the command line:

ruby -r minitest/pride clock_test.rb

Source

Pairing session with Erin Drummond https://twitter.com/ebdrummond

Submitting Incomplete Solutions

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

clock_test.rb

require 'minitest/autorun'
require_relative 'clock'

# Common test data version: 2.3.0 1680779
class ClockTest < Minitest::Test
  def test_on_the_hour
    # skip
    assert_equal "08:00", Clock.new(hour: 8).to_s
  end

  def test_past_the_hour
    skip
    assert_equal "11:09", Clock.new(hour: 11, minute: 9).to_s
  end

  def test_midnight_is_zero_hours
    skip
    assert_equal "00:00", Clock.new(hour: 24).to_s
  end

  def test_hour_rolls_over
    skip
    assert_equal "01:00", Clock.new(hour: 25).to_s
  end

  def test_hour_rolls_over_continuously
    skip
    assert_equal "04:00", Clock.new(hour: 100).to_s
  end

  def test_sixty_minutes_is_next_hour
    skip
    assert_equal "02:00", Clock.new(hour: 1, minute: 60).to_s
  end

  def test_minutes_roll_over
    skip
    assert_equal "02:40", Clock.new(minute: 160).to_s
  end

  def test_minutes_roll_over_continuously
    skip
    assert_equal "04:43", Clock.new(minute: 1723).to_s
  end

  def test_hour_and_minutes_roll_over
    skip
    assert_equal "03:40", Clock.new(hour: 25, minute: 160).to_s
  end

  def test_hour_and_minutes_roll_over_continuously
    skip
    assert_equal "11:01", Clock.new(hour: 201, minute: 3001).to_s
  end

  def test_hour_and_minutes_roll_over_to_exactly_midnight
    skip
    assert_equal "00:00", Clock.new(hour: 72, minute: 8640).to_s
  end

  def test_negative_hour
    skip
    assert_equal "23:15", Clock.new(hour: -1, minute: 15).to_s
  end

  def test_negative_hour_rolls_over
    skip
    assert_equal "23:00", Clock.new(hour: -25).to_s
  end

  def test_negative_hour_rolls_over_continuously
    skip
    assert_equal "05:00", Clock.new(hour: -91).to_s
  end

  def test_negative_minutes
    skip
    assert_equal "00:20", Clock.new(hour: 1, minute: -40).to_s
  end

  def test_negative_minutes_roll_over
    skip
    assert_equal "22:20", Clock.new(hour: 1, minute: -160).to_s
  end

  def test_negative_minutes_roll_over_continuously
    skip
    assert_equal "16:40", Clock.new(hour: 1, minute: -4820).to_s
  end

  def test_negative_hour_and_minutes_both_roll_over
    skip
    assert_equal "20:20", Clock.new(hour: -25, minute: -160).to_s
  end

  def test_negative_hour_and_minutes_both_roll_over_continuously
    skip
    assert_equal "22:10", Clock.new(hour: -121, minute: -5810).to_s
  end

  def test_add_minutes
    skip
    clock1 = Clock.new(hour: 10, minute: 0)
    assert_equal "10:03", (clock1 + Clock.new(minute: 3)).to_s
  end

  def test_add_no_minutes
    skip
    clock1 = Clock.new(hour: 6, minute: 41)
    assert_equal "06:41", (clock1 + Clock.new(minute: 0)).to_s
  end

  def test_add_to_next_hour
    skip
    clock1 = Clock.new(hour: 0, minute: 45)
    assert_equal "01:25", (clock1 + Clock.new(minute: 40)).to_s
  end

  def test_add_more_than_one_hour
    skip
    clock1 = Clock.new(hour: 10, minute: 0)
    assert_equal "11:01", (clock1 + Clock.new(minute: 61)).to_s
  end

  def test_add_more_than_two_hours_with_carry
    skip
    clock1 = Clock.new(hour: 0, minute: 45)
    assert_equal "03:25", (clock1 + Clock.new(minute: 160)).to_s
  end

  def test_add_across_midnight
    skip
    clock1 = Clock.new(hour: 23, minute: 59)
    assert_equal "00:01", (clock1 + Clock.new(minute: 2)).to_s
  end

  def test_add_more_than_one_day
    skip
    clock1 = Clock.new(hour: 5, minute: 32)
    assert_equal "06:32", (clock1 + Clock.new(minute: 1500)).to_s
  end

  def test_add_more_than_two_days
    skip
    clock1 = Clock.new(hour: 1, minute: 1)
    assert_equal "11:21", (clock1 + Clock.new(minute: 3500)).to_s
  end

  def test_subtract_minutes
    skip
    clock1 = Clock.new(hour: 10, minute: 3)
    assert_equal "10:00", (clock1 - Clock.new(minute: 3)).to_s
  end

  def test_subtract_to_previous_hour
    skip
    clock1 = Clock.new(hour: 10, minute: 3)
    assert_equal "09:33", (clock1 - Clock.new(minute: 30)).to_s
  end

  def test_subtract_more_than_an_hour
    skip
    clock1 = Clock.new(hour: 10, minute: 3)
    assert_equal "08:53", (clock1 - Clock.new(minute: 70)).to_s
  end

  def test_subtract_across_midnight
    skip
    clock1 = Clock.new(hour: 0, minute: 3)
    assert_equal "23:59", (clock1 - Clock.new(minute: 4)).to_s
  end

  def test_subtract_more_than_two_hours
    skip
    clock1 = Clock.new(hour: 0, minute: 0)
    assert_equal "21:20", (clock1 - Clock.new(minute: 160)).to_s
  end

  def test_subtract_more_than_two_hours_with_borrow
    skip
    clock1 = Clock.new(hour: 6, minute: 15)
    assert_equal "03:35", (clock1 - Clock.new(minute: 160)).to_s
  end

  def test_subtract_more_than_one_day
    skip
    clock1 = Clock.new(hour: 5, minute: 32)
    assert_equal "04:32", (clock1 - Clock.new(minute: 1500)).to_s
  end

  def test_subtract_more_than_two_days
    skip
    clock1 = Clock.new(hour: 2, minute: 20)
    assert_equal "00:20", (clock1 - Clock.new(minute: 3000)).to_s
  end

  def test_clocks_with_same_time
    skip
    clock1 = Clock.new(hour: 15, minute: 37)
    clock2 = Clock.new(hour: 15, minute: 37)
    assert clock1 == clock2
  end

  def test_clocks_a_minute_apart
    skip
    clock1 = Clock.new(hour: 15, minute: 36)
    clock2 = Clock.new(hour: 15, minute: 37)
    refute clock1 == clock2
  end

  def test_clocks_an_hour_apart
    skip
    clock1 = Clock.new(hour: 14, minute: 37)
    clock2 = Clock.new(hour: 15, minute: 37)
    refute clock1 == clock2
  end

  def test_clocks_with_hour_overflow
    skip
    clock1 = Clock.new(hour: 10, minute: 37)
    clock2 = Clock.new(hour: 34, minute: 37)
    assert clock1 == clock2
  end

  def test_clocks_with_hour_overflow_by_several_days
    skip
    clock1 = Clock.new(hour: 3, minute: 11)
    clock2 = Clock.new(hour: 99, minute: 11)
    assert clock1 == clock2
  end

  def test_clocks_with_negative_hour
    skip
    clock1 = Clock.new(hour: 22, minute: 40)
    clock2 = Clock.new(hour: -2, minute: 40)
    assert clock1 == clock2
  end

  def test_clocks_with_negative_hour_that_wraps
    skip
    clock1 = Clock.new(hour: 17, minute: 3)
    clock2 = Clock.new(hour: -31, minute: 3)
    assert clock1 == clock2
  end

  def test_clocks_with_negative_hour_that_wraps_multiple_times
    skip
    clock1 = Clock.new(hour: 13, minute: 49)
    clock2 = Clock.new(hour: -83, minute: 49)
    assert clock1 == clock2
  end

  def test_clocks_with_minute_overflow
    skip
    clock1 = Clock.new(hour: 0, minute: 1)
    clock2 = Clock.new(hour: 0, minute: 1441)
    assert clock1 == clock2
  end

  def test_clocks_with_minute_overflow_by_several_days
    skip
    clock1 = Clock.new(hour: 2, minute: 2)
    clock2 = Clock.new(hour: 2, minute: 4322)
    assert clock1 == clock2
  end

  def test_clocks_with_negative_minute
    skip
    clock1 = Clock.new(hour: 2, minute: 40)
    clock2 = Clock.new(hour: 3, minute: -20)
    assert clock1 == clock2
  end

  def test_clocks_with_negative_minute_that_wraps
    skip
    clock1 = Clock.new(hour: 4, minute: 10)
    clock2 = Clock.new(hour: 5, minute: -1490)
    assert clock1 == clock2
  end

  def test_clocks_with_negative_minute_that_wraps_multiple_times
    skip
    clock1 = Clock.new(hour: 6, minute: 15)
    clock2 = Clock.new(hour: 6, minute: -4305)
    assert clock1 == clock2
  end

  def test_clocks_with_negative_hours_and_minutes
    skip
    clock1 = Clock.new(hour: 7, minute: 32)
    clock2 = Clock.new(hour: -12, minute: -268)
    assert clock1 == clock2
  end

  def test_clocks_with_negative_hours_and_minutes_that_wrap
    skip
    clock1 = Clock.new(hour: 18, minute: 7)
    clock2 = Clock.new(hour: -54, minute: -11513)
    assert clock1 == clock2
  end

  def test_full_clock_and_zeroed_clock
    skip
    clock1 = Clock.new(hour: 24, minute: 0)
    clock2 = Clock.new(hour: 0, minute: 0)
    assert clock1 == clock2
  end
end
module BookKeeping
  VERSION = 2
end

class Clock
  attr_accessor :hours, :minutes
  DAY = 24
  HOUR = 60
  private_constant :DAY, :HOUR

  def initialize(hours, minutes)
    @hours = hours
    @minutes = minutes
    rollover_minutes
  end

  def self.at(hours, minutes)
    new(hours, minutes)
  end

  def to_s
    format '%02i:%02i', @hours, @minutes
  end

  def ==(other)
    @hours == other.hours && @minutes == other.minutes
  end

  def +(other)
    @minutes += other
    rollover_minutes
    self
  end

  private

  def rollover_hours
    if @hours.negative?
      @hours = DAY - -@hours % DAY
    else
      @hours -= @hours / DAY * DAY
    end
    @hours = 0 if @hours == DAY
  end

  def rollover_minutes
    minutes = @minutes
    if @minutes.negative?
      @minutes = HOUR - -@minutes % HOUR
    else
      @minutes -= @minutes / HOUR * HOUR
    end
    @hours += minutes / HOUR
    rollover_hours
  end
end

What can you learn from this solution?

A huge amount can be learnt from reading other people’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 I could read more about to develop my understanding?