2025 Advent of Code

This repository contains my solutions for the Advent of Code 2025 programming puzzles, implemented in Go, a language I am currently learning.

Each day lives in its own folder (day_1, day_2, day_3, day_4, …) with its own go.mod, a small command-line entrypoint under cmd/, and an internal package that holds the core logic.

Structure

• day_1/ – solution for Day 1 (dial rotations). See day_1/README.md for full details.
• day_2/ – solution for Day 2 (invalid product ID ranges). See day_2/README.md for full details.
• day_3/ – solution for Day 3 (battery banks, 12-digit greedy voltage). See day_3/README.md for full details.
• day_4/ – solution for Day 4 (accessible rolls removal using a forklift). See day_4/README.md for full details.
• day_5/ – solution for Day 5 (fresh ingredient ranges with compaction). See day_5/README.md for full details.
• day_6/ – solution for Day 6 (column-wise arithmetic with cell transposition). See day_6/README.md for full details.
• day_7/ – solution for Day 7 (multiverse timeline splitter with tachyon beams). See day_7/README.md for full details.
• day_8/ – solution for Day 8 (junction box playground wiring). See day_8/README.md for full details.
• day_9/ – solution for Day 9 (movie theater seating and largest rectangle). See day_9/README.md for full details.
• day_10/ – solution for Day 10 (factory machine joltage configuration using Hermite Normal Form). See day_10/README.md for full details.
• day_11/ – solution for Day 11 (reactor device graph with constrained path counting). See day_11/README.md for full details.
• day_12/ – solution for Day 12 (packing weird-shaped presents under Christmas trees). See day_12/README.md for full details.

Each day generally includes:

• An input.txt file containing the puzzle input.
• A Makefile with convenience targets to run the solution.
• Unit tests under internal/... validating the core logic.

Running a day

To run a given day, cd into the corresponding folder and either use make:

cd day_1
make run ARGS="input.txt"

or call go run directly on the command:

cd day_1
go run ./cmd input.txt

Replace day_1 with day_2, day_3, day_4, … to run other days.