This year’s Advent of Code is well past the half-way mark, and I’ve been reflecting on some of the harder or more interesting problems over the last few years, and the lessons learned about making code faster, or large problems tractable.

In case you haven’t encountered it, AoC is an annual coding competition, with a new problem every day, from December 1 through 25. Each day, there are two parts, and the second (usually harder) part unlocks after you solve the first part. You can use any programming language, and only need to submit the right answer (usually a number) to solve each part.