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to Leap in the Scala Track

Published at Jan 18 2019 · 0 comments
Test suite

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.


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.


Try to avoid code repetition, use private helper functions if you can.

And you might consider using a single Boolean expression instead of if-else for better readability. See here on how this could be done (the link is for Java, but of course the logic is valid for Scala, too).

The Scala exercises assume an SBT project scheme. The exercise solution source should be placed within the exercise directory/src/main/scala. The exercise unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command sbt test in the exercise directory.

For more detailed info about the Scala track see the help page.


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.


import org.scalatest.{Matchers, FunSuite}

/** @version 1.3.0 */
class LeapTest extends FunSuite with Matchers {

  test("year not divisible by 4: common year") {
    Leap.leapYear(2015) should be (false)

  test("year divisible by 4, not divisible by 100: leap year") {
    Leap.leapYear(1996) should be (true)

  test("year divisible by 100, not divisible by 400: common year") {
    Leap.leapYear(2100) should be (false)

  test("year divisible by 400: leap year") {
    Leap.leapYear(2000) should be (true)
object Leap {
  def leapYear(year: Int): Boolean =
    year % 4 == 0 && (year % 100 != 0 || year % 400 == 0)

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