Advent of Code 2025

My solution in Zig

This year I want to complete each day without brute force. I will see how long that lasts.

Instructions

Before building: Download inputs.

For day 1, go to https://adventofcode.com/2025/day/1/input to see your input for the day. ctrl+a and copy paste into day01/input.txt.

The process is the same for the other days.

Building

Make sure you have Zig 0.15

To build a specific day, cd into that day's folder, and run:

zig build

To run the executable, use either

zig build run

or

./zig-out/bin/adventofcode

To build with optimizations, run

zig build -Doptimize=ReleaseFast

Bechmarking

The root folder has its own build script, running zig build in the root folder will build all day's solutions.

Running the time step will use hyperfine to time each day's solution. I will try my best to keep each day under 1ms on my laptop.

zig build -Doptimize=ReleaseFast time

Speed

These are the speeds on my laptop.

day	Time (mean ± σ)	Range (min … max)
1	285.8 µs ± 79.7 µs	147.4 µs … 1476.6 µs
2	355.2 µs ± 92.7 µs	190.6 µs … 1679.4 µs
3	218.9 µs ± 69.3 µs	130.3 µs … 1495.9 µs
4	490.9 µs ± 111.6 µs	228.9 µs … 1994.8 µs
5	377.8 µs ± 112.9 µs	210.2 µs … 1877.2 µs
6	341.4 µs ± 87.2 µs	167.7 µs … 1648.7 µs
7	172.5 µs ± 57.8 µs	110.3 µs … 1407.7 µs