AoC puzzle set of 2023 was considerably harder than previous couple of years (last comparable year in terms of difficulty is 2019, I'd say). Rumors have it, that it started heavier to cope with the raise of the robots (err LLMs I mean). Then the difficulty hit plateau for a while, after the final ascend to rarely seen heights. It was a plethora of graph traversing puzzles, mathematic and combinatoric ones.
Some of the puzzles were, in my humble opinion, a bit flawed. Prime example is day 21, where the actual input had vastly different (but crucial) properties than the example one.
Day 24 was easily solvable by famous Z3 Theorem Prover software package. Otherwise, it was exceptionally hard. Yes, it could be brute-forced (if done in the right way) as well, and there is a basic linear-algebra-powered observation that can be done to reduce the problem to system of 6 linear equations for 6 unknowns, but still. Another puzzle, where visualization helps.
Day 25 is a funny one, as it is a bare bone classical problem in CS - minimum cut of an undirected graph. Some toolkits have a ready-made solver for this, other don't. And we either get very clever or have to visualize the problem and find the solution from the image.
Puzzles with exceptional entertainment value and/or unconventional thinking necessary fit the highlights for me. Usually the most fun/challenging experience is hidden in Part 2 of the puzzle.
TBD.
