Advent of Code 2025

This repository contains my solutions for the Advent of Code 2025 in Rust.

Unlike last year, this year, I have decided to take a different approach in organizing my solutions:

• Each day's solution is contained within its own crate (e.g., day01, day02, etc.), so that multiple files for a single day can be possible.
• A shared utility crate (util) is created to hold common functionalities used across different days, such as input reading and parsing.
• No more top-level binary crate; instead, each day's crate is a binary crate itself. This also means no more macro-based solution definition.
• A workspace is set up to manage all the crates together. Testing and building can be done from the workspace root.

The core idea is to leverage Rust's crate system and Cargo's workspace feature to reduce the boilerplate and improve code organization.

Performance

Although not the primary focus of my solutions, I tried my best to find the most efficient approach to each day's puzzle, which might take advantage of certain structures of the problem input thus not directly comparable with general solution to the described problem.

Below are the benchmarking result of different part of the solutions, ran on M1 max with 64G RAM. The median $\pm$ MAD of runtimes are reported. The results are quite satisfactory, with a total runtime around 150 ms for all 12 days' puzzles on my machine.

Day	Parsing	Part 1	Part 2	Note
01	111.125 $\pm$ 2.167 µs	18.250 $\pm$ 0.042 µs	20.667 $\pm$ 0.042 µs
02	30.292 $\pm$ 1.375 µs	16.625 $\pm$ 3.584 µs	29.167 $\pm$ 4.750 µs	Prime factors decomposition
03	158.395 $\pm$ 3.103 µs	96.875 $\pm$ 12.750 µs	200.000 $\pm$ 15.042 µs	Dynamic programming
04	180.209 $\pm$ 2.709 µs	111.583 $\pm$ 11.792 µs	12.038 $\pm$ 0.284 ms
05	70.625 $\pm$ 1.375 µs	23.542 $\pm$ 5.000 µs	19.584 $\pm$ 4.582 µs	Binary search
06	107.375 $\pm$ 2.375 µs	40.625 $\pm$ 6.250 µs	117.583 $\pm$ 9.625 µs
07	816.396 $\pm$ 41.666 µs	3.375 $\pm$ 0.042 µs	3.083 $\pm$ 0.042 µs	Dynamic programming (I guess)
08	227.083 $\pm$ 3.458 µs	698.417 $\pm$ 4.292 µs	24.027 $\pm$ 0.102 ms	Octree + Branch and Bound
09	67.145 $\pm$ 2.979 µs	2.552 $\pm$ 0.243 ms	9.382 $\pm$ 0.942 ms	Intersection of edges
10	192.104 $\pm$ 4.062 µs	439.562 $\pm$ 38.729 µs	90.178 $\pm$ 2.595 ms	Divide and conquer
11	311.895 $\pm$ 5.395 µs	1.359 $\pm$ 0.105 ms	1.293 $\pm$ 0.060 ms	Dynamic programming
12	163.166 $\pm$ 4.333 µs	48.458 $\pm$ 7.625 µs	N/A	😅

License

This project is licensed under the MIT OR Apache-2.0 License. See the LICENSE-MIT and LICENSE-APACHE files for details.