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4d47's solution

to Leap in the PHP Track

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 the tests

  1. Go to the root of your PHP exercise directory, which is <EXERCISM_WORKSPACE>/php. To find the Exercism workspace run

     % exercism debug | grep Workspace
    
  2. Get PHPUnit if you don't have it already.

     % wget --no-check-certificate https://phar.phpunit.de/phpunit.phar
     % chmod +x phpunit.phar
    
  3. Execute the tests:

     % ./phpunit.phar leap/leap_test.php
    

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.php

<?php

require "leap.php";

class YearTest extends PHPUnit\Framework\TestCase
{
    public function testLeapYear()
    {
        $this->assertTrue(isLeap(1996));
    }

    public function testNonLeapYear()
    {
        $this->markTestSkipped();
        $this->assertFalse(isLeap(1997));
    }

    public function testNonLeapEvenYear()
    {
        $this->markTestSkipped();
        $this->assertFalse(isLeap(1998));
    }

    public function testCentury()
    {
        $this->markTestSkipped();
        $this->assertFalse(isLeap(1900));
    }

    public function testFourthCentury()
    {
        $this->markTestSkipped();
        $this->assertTrue(isLeap(2400));
    }
}
<?php


function divides($divisor, $dividend) {
    return $dividend % $divisor === 0;
}

function isLeap($year)
{
    return divides(4, $year) && (!divides(100, $year) || divides(400, $year));
}

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?