This is where I'll be throwing all of my Advent of Code work. Spoilers if you're doing it yourself, I guess.
Because I assume that code reuse will be valuable, the repository is divided by language at the top level, with years and days nested underneath each language directory. This allows (for example) all of the Go code to be a single module containing multiple packages, so that a Day 5 solution can import the Day 1 solution as a dependency.