I've been working my way through the questions here slowly-and-steadily, in my free time and as an exercise to "keep my hand in" during periods I'm not doing a ton of work coding or just want to be able to hack away with less constraints.
Language is Kotlin, approach in terms of software engineering rigour is "good enough" - I don't like to write trash code, but once each puzzle is solved, we know the code is correct and unlikely to be worked on further (and will never be collaborated on), so gold-plating in terms of deep refactoring, very high test coverage etc is fairly pointless. Unit tests are generally there to help me reason through something at a more granular level, not to prevent regression :-)