Recommended to watch in a full-screen and on 720p or higher quality.

Script

Hello, hello! I am Oleksii Fedorov, and this is the third episode of TDD Screencast.

In last episode we have implemented a sorting algorithm using TDD, without thinking about algorithm beforehand. As a result, bubble sort have emerged.

We have noticed, that there is a small weird thing about this implementation: it has unspecified behavior - mutation of the original array.

So we asked, which algorithm would emerge, if we were to ban such side-effects from our algorithm. Let’s find out!

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./watch.sh
vim           # implement sorting algorithm

I think we are done here. If you look closely, it is a quicksort. It is not the most memory-efficient implementation, but that is something that is simple to optimize (instead of passing recursively arrays, pass original array and indexes). That optimization will involve actual mutation of the array in place, so if we want to stay true to our specification /show test for no-side-effects/. We will have to copy the array once, using some sort of wrapper function.

Applying this optimization I leave as an exercise to you my users.

In the next episode we will look into path-finding problem, and we will see, how these techniques apply there. See you next time! Have a nice day.