One of my hobbies is to try out some Project Euler problems. It is a great way to practice your creative and coding skills at the same time you have fun and relax a little bit.
If you don't understand what I'm talking about check out the following link:
https://projecteuler.net/about

What I look for when I'm solving one of these problems is to minimize 3 things:

1. Libraries I use.
2. Lines of code.
3. Execution time.