Adventures in Advent of Code
I’ve been participating regularly in Advent of Code for the past couple of years. It’s one of the highlights of my holiday season. The puzzles are fun, the stories are appropriately ridiculous, and it’s a neat way for me to keep the cobwebs brushed off some of the things I learned years ago that I don’t regularly use. Every year there are puzzles that take me a couple of minutes to solve, and puzzles that take me hours: I will forever curse the Intcode puzzles from 2019.
Last night’s puzzle was something new. The problem itself was pretty straight-forward (finding values that are common in multiple collections), but it resulted in a 45-minute debugging session that culminated in finding a bug in Swift’s implementation of Set.intersection(_:).
The nature of last night’s problem was that, when I had a bunch of inputs, I could expect that there was only a single common element between all of them. After getting lucky and solving the problem correctly, I started golfing my code to make it terser. That’s when I started noticing something odd.
