Advent of Code

This repo contains my solutions for Advent of Code. Each solution includes a short write-up explaining my approach.

So far I've only done 2024, in Zig. I might do other years in other languages later, or I might not.

Also see the accompanying blog post.

Solutions

Each day links to the source code and the accompanying write-up.

Day	Title	Solution	Write up	Benchmark (ReleaseFast, µs)
1	Historian Hysteria	Code	Write up	41.8
2	Red-Nosed Reports	Code	Write up	54.4
3	Mull it Over	Code	Write up	23.2
4	Ceres Search	Code	Write up	5.9
5	Print Queue	Code	Write up	26.9
6	Guard Gallivant	Code	Write up	24,370.7
7	Bridge Repair	Code	Write up	10,014.7
8	Resonant Collinearity	Code	Write up	19.4
9	Disk Fragmenter	Code	Write up	151.7
10	Hoof It	Code	Write up	59.9
11	Plutonian Pebbles	Code	Write up	2,159.1
12	Garden Groups	Code	Write up	420.3
13	Claw Contraption	Code	Write up	14.7
14	Restroom Redoubt	Code	Write up	13.7
15	Warehouse Woes	Code	Write up	701.5
16	Reindeer Maze	Code	Write up	11,504.1
17	Chronospatial Computer	Code	Write up	44.8
18	RAM Run	Code	Write up	85.2
19	Linen Layout	Code	Write up	23,810.2
20	Race Condition	Code	Write up	157.4
21	Keypad Conundrum	Code	Write up	24.2
22	Monkey Market	Code	Write up	11,248.4
23	LAN Party	Code	Write up	38.2
24	Crossed Wires	Code	Write up	60.7
25	Code Chronicle	Code	Write up	24.9

Benchmarks

Benchmarks are done on a Apple M3 Pro using this bash script. Each puzzle has separate measurements for parsing, part 1, and part 2.

Optimize mode: Debug

Total runtime: 1,242.9 ms.

Benchmarks

Day	Title	Parsing (µs)	Part 1 (µs)	Part 2 (µs)	Total (µs)
1	Historian Hysteria	361.4	256.9	8.1	626.4
2	Red-Nosed Reports	598.2	33.8	91.2	723.2
3	Mull it Over	0.0	110.3	119.7	230.1
4	Ceres Search	67.7	4,849.7	1,093.7	6,011.2
5	Print Queue	361.5	8.8	95.1	465.4
6	Guard Gallivant	124.8	77.3	104,955.0	105,157.1
7	Bridge Repair	730.0	2,921.5	140,020.8	143,672.3
8	Resonant Collinearity	54.2	90.3	383.5	528.0
9	Disk Fragmenter	49.1	125.1	1,434.8	1,609.1
10	Hoof It	25.1	409.9	252.0	686.9
11	Plutonian Pebbles	1.0	933.6	32,657.6	33,592.2
12	Garden Groups	67.6	1,224.6	1,794.9	3,087.2
13	Claw Contraption	256.6	7.1	7.1	270.8
14	Restroom Redoubt	247.0	9.9	114,785.9	115,042.7
15	Warehouse Woes	311.0	634.5	1,103.9	2,049.4
16	Reindeer Maze	153.9	15,397.6	48,751.2	64,302.7
17	Chronospatial Computer	1.6	1.2	290.5	293.3
18	RAM Run	592.9	326.8	437.6	1,357.3
19	Linen Layout	127.0	207,814.8	207,684.8	415,626.6
20	Race Condition	325.1	2,164.6	93,134.5	95,624.2
21	Keypad Conundrum	0.7	41.4	566.2	608.2
22	Monkey Market	319.0	79,065.1	168,422.9	247,807.0
23	LAN Party	143.4	523.9	11.4	678.7
24	Crossed Wires	79.3	1,615.4	262.1	1,956.9
25	Code Chronicle	696.7	189.1	0.0	885.9

Optimize mode: ReleaseSafe

Total runtime: 146.1 ms.

Benchmarks

Day	Title	Parsing (µs)	Part 1 (µs)	Part 2 (µs)	Total (µs)
1	Historian Hysteria	24.5	18.5	2.9	46.0
2	Red-Nosed Reports	55.4	4.5	15.5	75.4
3	Mull it Over	0.0	9.4	14.2	23.6
4	Ceres Search	6.7	41.8	21.4	69.9
5	Print Queue	22.5	1.2	6.0	29.7
6	Guard Gallivant	20.2	12.3	13,156.5	13,189.0
7	Bridge Repair	67.4	437.4	12,760.7	13,265.5
8	Resonant Collinearity	3.3	4.5	18.5	26.3
9	Disk Fragmenter	6.8	25.4	234.3	266.5
10	Hoof It	3.4	42.7	37.7	83.8
11	Plutonian Pebbles	0.1	47.8	2,548.1	2,596.1
12	Garden Groups	6.9	258.1	368.4	633.5
13	Claw Contraption	18.8	0.9	0.9	20.5
14	Restroom Redoubt	15.2	2.0	20,863.8	20,881.1
15	Warehouse Woes	77.5	212.3	461.0	750.7
16	Reindeer Maze	49.2	4,676.7	15,408.5	20,134.4
17	Chronospatial Computer	0.1	0.2	42.0	42.3
18	RAM Run	43.3	23.5	62.6	129.4
19	Linen Layout	11.4	12,983.8	12,979.9	25,975.1
20	Race Condition	56.0	427.5	25,316.8	25,800.4
21	Keypad Conundrum	0.1	2.7	33.0	35.7
22	Monkey Market	22.7	5,660.8	16,055.8	21,739.4
23	LAN Party	16.6	25.3	2.6	44.5
24	Crossed Wires	8.4	91.7	16.8	116.9
25	Code Chronicle	45.2	66.8	0.0	112.1

Optimize mode: ReleaseFast

Total runtime: 85.1 ms.

Benchmarks

Day	Title	Parsing (µs)	Part 1 (µs)	Part 2 (µs)	Total (µs)
1	Historian Hysteria	23.5	15.5	2.8	41.8
2	Red-Nosed Reports	42.9	0.0	11.5	54.4
3	Mull it Over	0.0	7.2	16.0	23.2
4	Ceres Search	5.9	0.0	0.0	5.9
5	Print Queue	22.3	0.0	4.6	26.9
6	Guard Gallivant	14.0	25.2	24,331.5	24,370.7
7	Bridge Repair	72.6	321.4	9,620.7	10,014.7
8	Resonant Collinearity	2.7	3.3	13.4	19.4
9	Disk Fragmenter	0.8	12.9	137.9	151.7
10	Hoof It	2.2	29.9	27.8	59.9
11	Plutonian Pebbles	0.1	43.8	2,115.2	2,159.1
12	Garden Groups	6.8	164.4	249.0	420.3
13	Claw Contraption	14.7	0.0	0.0	14.7
14	Restroom Redoubt	13.7	0.0	0.0	13.7
15	Warehouse Woes	14.6	228.5	458.3	701.5
16	Reindeer Maze	12.6	2,480.8	9,010.7	11,504.1
17	Chronospatial Computer	0.1	0.2	44.5	44.8
18	RAM Run	35.6	15.8	33.8	85.2
19	Linen Layout	10.7	11,890.8	11,908.7	23,810.2
20	Race Condition	48.7	54.5	54.2	157.4
21	Keypad Conundrum	0.0	1.7	22.4	24.2
22	Monkey Market	20.7	0.0	11,227.7	11,248.4
23	LAN Party	13.6	22.0	2.5	38.2
24	Crossed Wires	5.0	41.3	14.3	60.7
25	Code Chronicle	24.9	0.0	0.0	24.9

Optimize mode: ReleaseSmall

Total runtime: 139.35 ms.

Benchmarks

Day	Title	Parsing (µs)	Part 1 (µs)	Part 2 (µs)	Total (µs)
1	Historian Hysteria	30.1	17.8	2.6	50.6
2	Red-Nosed Reports	59.2	3.3	14.4	76.8
3	Mull it Over	0.0	15.4	20.7	36.1
4	Ceres Search	6.8	634.8	118.4	760.0
5	Print Queue	30.5	1.0	6.1	37.5
6	Guard Gallivant	14.8	34.1	26,542.4	26,591.4
7	Bridge Repair	93.2	886.4	26,021.9	27,001.5
8	Resonant Collinearity	4.5	6.7	28.2	39.3
9	Disk Fragmenter	6.2	15.6	149.0	170.8
10	Hoof It	3.0	51.9	37.7	92.6
11	Plutonian Pebbles	0.1	68.2	2,797.4	2,865.7
12	Garden Groups	7.8	189.2	252.5	449.4
13	Claw Contraption	20.5	0.0	0.0	20.5
14	Restroom Redoubt	39.1	0.1	1,358.3	1,397.5
15	Warehouse Woes	16.6	257.4	503.1	777.1
16	Reindeer Maze	46.9	2,665.8	9,338.2	12,050.9
17	Chronospatial Computer	0.2	0.3	69.1	69.6
18	RAM Run	71.7	25.2	43.0	139.9
19	Linen Layout	21.8	25,477.8	25,483.3	50,982.9
20	Race Condition	60.2	65.2	66.2	191.7
21	Keypad Conundrum	0.1	2.1	27.9	30.1
22	Monkey Market	23.6	0.0	15,141.3	15,164.8
23	LAN Party	11.2	42.8	2.6	56.6
24	Crossed Wires	10.4	204.6	23.2	238.1
25	Code Chronicle	60.3	0.0	0.0	60.4

Self-imposed constraints

To make things a little more interesting, I set a few constraints and rules for myself:

1. The code must be readable. By "readable", I mean the code should be straightforward and easy to follow. No unnecessary abstractions. I should be able to come back to the code months later and still understand (most of) it.
2. Solutions must be a single file. No external dependencies. No shared utilities module. Everything needed to solve the puzzle should be visible in that one solution file.
3. The total runtime must be under one second. All solutions when run sequentially should finish in under one second. I want to improve my performance engineering skills.
4. Parts should be solved separately. This means: (1) no solving both parts simultaneously, and (2) no doing extra work in part one that make part two faster. The aim of this is to get a clear idea of how long each part takes on its own.
5. No concurrency or parallelism. Solutions must run sequentially on a single thread. This keeps the focus on the efficiency of the algorithm. I can't speed up slow solutions by using multiple CPU cores.
6. No ChatGPT. No Claude. No AI help. I want to train myself, not the LLM. I can look at other people's solutions, but only after I have given my best effort at solving the problem.
7. Follow the constraints of the input file. The solution doesn't have to work for all possible scenarios, but it should work for all other inputs; if the input file only contains 8-bit unsigned integers, it doesn't have to handle larger integer types.
8. Hardcoding is allowed. For example: size of the input, number of rows and columns, etc. Since the input is known at compile-time, we can skip runtime parsing and just embed it into the program using Zig's @embedFile.

Local development setup

To run the solutions, you'll first need to place your input files in the src/days/data/ directory with the format dayXX.txt (add leading zeros for days 1-9). This project uses the Zig build system to run the commands.

Below are a list of the available commands. For the run and bench steps, you can also pass the optimize mode with the -Doptimize flag.

Building

• zig build - Builds all of the binaries. This is useful if you just want to compile without running the programs.

Running

• zig build run - Runs all solution sequentially.
• zig build run -Day=XX - Runs the solution for a single day.

Benchmarking

• zig build bench - Benchmarks all solutions sequentially.
• zig build bench -Day=XX - Benchmarks the solution for a single day.

Testing

• zig build test - Tests all solutions sequentially.
• zig build test -Day=XX - Tests the solution for a single day.