A programming kata is an exercise which helps a programmer hone his skills through practice and repetition.

This article is part of the series "Scala Tutorial Through Katas". Articles are divided into easy, medium and hard. Beginners should start with easy ones and move towards more complicated once they feel more comfortable programming in Scala.

For the complete list of Scala katas and solutions please visit the index page

The article assumes that the reader is familiar with the basic usage of ScalaTest and knows how to run them from his favorite Scala IDE (ours is IntelliJ IDEA with the Scala plugin).

Tests that prove that the solution is correct are displayed below. Recommended way to solve this kata is to write the implementation for the first test, confirm that it passes and move to the next. Once all of the tests pass, the kata can be considered solved.

One possible solution is provided below the tests. Try to solve the kata by yourself first.

# Berlin Clock

Create a representation of the Berlin Clock for a given time (hh::mm:ss).

The Berlin Uhr (Clock) is a rather strange way to show the time.

On the top of the clock there is a yellow lamp that blinks on/off every two seconds.

The time is calculated by adding rectangular lamps.

The top two rows of lamps are red. These indicate the hours of a day. In the top row there are 4 red lamps.

Every lamp represents 5 hours. In the lower row of red lamps every lamp represents 1 hour.

So if two lamps of the first row and three of the second row are switched on that indicates 5+5+3=13h or 1 pm.

The two rows of lamps at the bottom count the minutes. The first of these rows has 11 lamps, the second 4.

In the first row every lamp represents 5 minutes.

In this first row the 3rd, 6th and 9th lamp are red and indicate the first quarter, half and last quarter of an hour.

The other lamps are yellow. In the last row with 4 lamps every lamp represents 1 minute.

The lamps are switched on from left to right.

Y = Yellow

R = Red

O = Off

[TESTS]

Test code can be found in the GitHub BerlinClock.scala.

[ONE POSSIBLE SOLUTION]

The solution code can be found in BerlinClock.scala solution.

What was your solution? Post it as a comment so that we can compare different ways to solve this kata.

Shai Yallin (@shaiyallin)My solution (admittedly a bit over-engineered but I wanted to make it pure functional):

https://github.com/electricmonk/scala-katas/blob/master/src/main/scala/com/shaiyallin/BerlinClock.scala

Ian Raytail-recursive solution to the topMinutes problem. I really like the 11 O’s and just drop to match the number of characters in acc.

def topMinutes(min: Int): String = {

def topMinutesAccumulator (min: Int, acc: String): String =

if(min topMinutesAccumulator(min – 5, acc + “R”)

case _ => topMinutesAccumulator(min – 5, acc + “Y”)

}

topMinutesAccumulator(min, “”)

}

Ian RayIt crushed my code for some reason. No matter:

def topMinutes(min: Int): String = {

def topMinutesAccumulator (min: Int, acc: String): String =

if(min topMinutesAccumulator(min – 5, acc + “R”)

case _ => topMinutesAccumulator(min – 5, acc + “Y”)

}

topMinutesAccumulator(min, “”)

}

Ian RayWell, pull it apart with an html tool lol you see what I meant.