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to Leap in the Ruby Track

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

Given a year, report if it is a leap year.

The tricky thing here is that a leap year in the Gregorian calendar occurs:

on every year that is evenly divisible by 4
  except every year that is evenly divisible by 100
    unless the year is also evenly divisible by 400

For example, 1997 is not a leap year, but 1996 is. 1900 is not a leap year, but 2000 is.

If your language provides a method in the standard library that does this look-up, pretend it doesn't exist and implement it yourself.

Notes

Though our exercise adopts some very simple rules, there is more to learn!

For a delightful, four minute explanation of the whole leap year phenomenon, go watch this youtube video.


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 leap_test.rb

To include color from the command line:

ruby -r minitest/pride leap_test.rb

Source

JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp

Submitting Incomplete Solutions

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

leap_test.rb

require 'minitest/autorun'
require_relative 'leap'

# Common test data version: 1.4.0 3134d31
class Date
  def leap?
    raise RuntimeError, "Implement this yourself instead of using Ruby's implementation."
  end

  alias gregorian_leap? leap?
  alias julian_leap? leap?
end

class YearTest < Minitest::Test
  def test_year_not_divisible_by_4_common_year
    # skip
    refute Year.leap?(2015), "Expected 'false', 2015 is not a leap year."
  end

  def test_year_divisible_by_4_not_divisible_by_100_leap_year
    skip
    assert Year.leap?(1996), "Expected 'true', 1996 is a leap year."
  end

  def test_year_divisible_by_100_not_divisible_by_400_common_year
    skip
    refute Year.leap?(2100), "Expected 'false', 2100 is not a leap year."
  end

  def test_year_divisible_by_400_leap_year
    skip
    assert Year.leap?(2000), "Expected 'true', 2000 is a leap year."
  end

  def test_year_divisible_by_200_not_divisible_by_400_common_year
    skip
    refute Year.leap?(1800), "Expected 'false', 1800 is not a leap year."
  end
end
module Year
  LEAP_YEAR = 4
  private_constant :LEAP_YEAR
  CENTURIAL_YEAR = 100
  private_constant :CENTURIAL_YEAR
  LEAP_CYCLE_LENGTH = 400
  private_constant :LEAP_CYCLE_LENGTH

  module_function

  def leap?(year)
    leap_year?(year) && (non_centurial_year?(year) || leap_cycle_year?(year))
  end

  def leap_year?(year)
    (year % LEAP_YEAR).zero?
  end
  private_class_method :leap_year?

  def non_centurial_year?(year)
    (year % CENTURIAL_YEAR).nonzero?
  end
  private_class_method :non_centurial_year?

  def leap_cycle_year?(year)
    (year % LEAP_CYCLE_LENGTH).zero?
  end
  private_class_method :leap_cycle_year?
end

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