Monday, September 2, 2013

Codility adds bug-fixing tasks to its service

We have added bug-fixing tasks as a third type of task provided by our service – in addition to programming tasks and SQL tasks.

While programming tasks focus on testing a programmer’s ability to write a correct and efficient piece of code from scratch, and SQL tasks check their data management skills, the new bug-fixing tasks focus on a programmer’s ability to read, understand and maintain code.

In bug-fixing tasks, the candidate is presented with a task description together with a coded solution that contains a bug in its implementation. The goal is to find the bug and correct it by modifying no more than 2–3 lines of code.

In bug-fixing tasks, a programmer needs to:
  • read the problem description, 
  • understand the correct approach to the solution, 
  • find the bug in the given implementation, 
  • correct the bug, 
  • test the solution. 

We are delighted that a number of our clients were willing to beta-test our bug-fixing tasks and help us perfect them. We would like especially to acknowledge Grzegorz Olender from Nokia Solutions and Networks (NSN) and Cyprian Wronka from Cadence for their substantial contributions and support.

Grzegorz Olender, R&D Manager at Nokia Solutions and Networks (NSN) on Codility's bug-fixing tasks::
“In real commercial software projects, you seldom have unlimited freedom to implement everything from scratch. More often you need to cope with legacy solutions to some degree. From this perspective, Codility’s bug-fixing tasks offer an interesting extension for candidate assessment. The first live tests in our company realized their hidden potential. Some candidates try to understand the given solution and fix the bug. Others take a trial-and-error approach, adding or removing pieces of code at random with rather disappointing results. Codility’s bug-fixing tasks are definitely worthy of your attention if you are working with legacy code.”
Bug-fixing tasks have been added to all of our plans, and are thus available immediately to all of our customers. 

If you are not yet one of our customers, please feel free to have a little fun right now and try out one of our bug-fixing tasks in this demo: 

We hope these tasks will provide great value in your recruitment process. We encourage you to share your impressions, critiques and suggestions for improvement with us. Please feel free to get in touch directly with Marcin, our CSO, on  

Happy bug-fixing and recruiting!

Codility Team


  1. I scored 100 in JS even though I didn't add 'var' before candidate. this causes leaks!
    PS. redefinition of 'i'

  2. i couldn't do it while the clock was ticking but later on i scored 100%. Funny thing is, i forgot to set the language to java and the code ran apparently the same in C#...