Part 2 complicated it, but yes. I just built regexes on the fly for Part 1. I wonder if they mean Day 13. The underlying math is based on the Chinese Remainder Theorem, but it is solvable without knowing it (or, in my case, "knowing" it, once I saw others mention it it came back but my math degree was a long time ago). A solution could be discovered incrementally without knowing the math by trying to optimize the naive version.