There's a README.txt in each year with a one-line description of each day - grepping this might be useful for snippets of code or data-structures.

Common / generic data-structures and algorithms are in lib/

Sorted containers might be useful in the future: https://grantjenks.com/docs/sortedcontainers/

Some interesting algorithms here: https://github.com/dps/aoc/blob/main/utils.py