06 May 2010
Code Katas are small, relatively simple exercises designed to give you a problem to try and solve. I like to use them as a way to get my feet wet and help write something more interesting than "Hello World" but less complicated than "The Internet's Next Killer App".
Rick Minerich mentioned this one on his blog already, but here is the original "problem"/challenge as it was presented to me and which I in turn shot to him over a Twitter DM:
I have a list, say something like [4, 4, 4, 4, 2, 2, 2, 3, 3, 2, 2, 2, 2, 1, 1, 1, 5, 5], which consists of varying repetitions of integers. (We can assume that it's always numbers, and the use of the term "list" here is generic—it could be a list, array, or some other collection class, your choice.) The goal is to take this list of numbers, and "compress" it down into a (theoretically smaller) list of numbers in pairs, where the first of the pair is the occurrence number of the value, which is the second number. So, since the list above has four 4's, followed by three 2's, two 3's, four 2's, three 1's and two 5's, it should compress into [4, 4, 3, 2, 2, 3, 4, 2, 3, 1, 2, 5].
This is a pretty easy challenge, but I wanted to try and solve it in a functional mindset, which the challenger had never seen before. I also thought it made for an interesting challenge for people who've never programming in functional languages before, because it requires a very different approach than the imperative solution.
Extensions to the kata (a.k.a. "extra credit"):
By the way, some of the extension questions make the Kata somewhat interesting even for the imperative/O-O developer; have at, and let me know what you think.
Last modified 06 May 2010