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to Leap in the Elixir 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.

Running tests

Execute the tests with:

$ elixir leap_test.exs

Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant @tag :pending with a # symbol.

For example:

# @tag :pending
test "shouting" do
  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end

Or, you can enable all the tests by commenting out the ExUnit.configure line in the test suite.

# ExUnit.configure exclude: :pending, trace: true

For more detailed information about the Elixir track, please see the help page.

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.exs

if !System.get_env("EXERCISM_TEST_EXAMPLES") do
  Code.load_file("leap.exs", __DIR__)
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule LeapTest do
  use ExUnit.Case

  # @tag :pending
  test "vanilla leap year" do
    assert Year.leap_year?(1996)
  end

  @tag :pending
  test "any old year" do
    refute Year.leap_year?(1997), "1997 is not a leap year."
  end

  @tag :pending
  test "century" do
    refute Year.leap_year?(1900), "1900 is not a leap year."
  end

  @tag :pending
  test "exceptional century" do
    assert Year.leap_year?(2400)
  end
end
defmodule Year do
  @doc """
  Returns whether 'year' is a leap year.

  A leap year 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
  """
  @spec leap_year?(non_neg_integer) :: boolean
  def leap_year?(y), do: rem(y,4) == 0 and (rem(y,100) != 0 or rem(y,400) == 0)
end

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