thekeele's solution

to Leap in the Elixir Track

Published at Nov 05 2019 · 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:

``````\$ mix test
``````

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
``````

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

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

``````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``````

test_helper.exs

``````ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)``````
``````defmodule Year do
@spec leap_year?(non_neg_integer) :: boolean

defguard is_leap_year?(year)
when rem(year, 400) === 0
or rem(year, 100) !== 0
and rem(year, 4) === 0

def leap_year?(year) when is_leap_year?(year), do: true
def leap_year?(_), do: false
end``````