These are my solutions to the Advent of Code challenges for 2021 and 2022.
They are all in Kotlin and use a mixture of approaches. Generally, I prefer to use immutable data structures and a functional programming style, but you'll also find some OO, pure procedural and mutable data in use too. Sometimes, that's just the simplest way to solve the problem. And simple and understandable trumps "clever". Having said that, some of the code might well be be over-complex for what it's trying to do ...
There are usually some tests for each day's solution, although the final arbiter of success is submission to the AoC site itself. I haven't included my input files as you can get your own set from the site.