Code Kata

Over the course of interviewing for a coding job, you’ll be required to prove that you actually know how to write code. This is usually by solving a problem of some kind. This might be a take-home challenge, a pair-programming exercise, or even (shudder) coding on a whiteboard. Obviously, you’ll want to practice these kinds of problems.

Many of the problems used in interviews can be found online in the form of a code kata. The name code kata comes from the kata in martial arts. In martial arts this involves practicing a set of moves repeatedly until they become like a reflex. Here’s the definition of a code kata on Wikipedia:

an exercise in programming which helps programmers hone their skills through practice and repetition.

I’m not really happy with that definition. To me, a code kata is different in that you shouldn’t repeat the same problem. Instead, solve a variety of challenges to build your problem-solving and coding skills. Of course, if you aren’t happy with a solution, refactor it or even start over, but I feel like the biggest gain comes from solving a many different problems.


So, where do you find these problems? Here are a few websites I’ve used in the past:

Project Euler has hundreds of challenging mathematical and computer programming problems. If you work your way through this list, you’ll be ready for anything. Many of these will be too difficult for a beginning programmer.

CodeKata is a site by PragDave (aka Dave Thomas of the Pragmatic Programmers). According to Wikipedia, Dave Thomas was probably the first person to use the term code kata. This site has a collection of 21 challenges.

Exercism has a collection of practice problems in over 30 different programming languages. If you only visit one site on this list, start here. After you submit your solution, you can see other users solutions and give and receive feedback.


The sites above involve solving a problem of some kind, but The Gilded Rose kata is all about refactoring. You’re given a program and asked to add a feature. Unfortunately, the program is poorly written and has no tests. Rather than just add the new feature, you’re expected to also clean up the program.

After you try the kata on your own, check out the talk All the Little Things by Sandi Metz at RailsConf 2014. Sandi Metz is the author of the highly recommended book Practical Object-Oriented Design in Ruby and a great speaker. If you’re a Ruby developer, you should watch all of her talks (assuming you haven’t already seen them).

What is your experience with practice problems? Did I miss a great code kata resource? Do you think this is all a waste of time? I’d love to hear your thoughts about coding challenges such as these.