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https://github.com/fabmax/aoc-2023

🎅 ☃️ Advent of code 2023 in Kotlin! 🎁 🎄
https://github.com/fabmax/aoc-2023

advent-of-code adventofcode aoc-2023-in-kotlin

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🎅 ☃️ Advent of code 2023 in Kotlin! 🎁 🎄

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# Advent of code 2023 (in kotlin)



Solutions to all puzzles of [Advent of code 2023](https://adventofcode.com/2023/)



I was awarded ["community star"](https://blog.jetbrains.com/kotlin/2024/02/advent-of-code-in-kotlin-2023-winners/)

by JetBrains :smile:



## Results



All [solutions](src/main/kotlin/y2023) work for both parts. There are a few notable days:



- **[Day 5:](src/main/kotlin/y2023/day05/Day05.kt) If You Give A Seed A Fertilizer**

  

  Part2 got pretty difficult. I took the lazy option and brute-forced it.

  The result for part 2 takes about 1 minute to compute.



- **[Day 10:](src/main/kotlin/y2023/day10/Day10.kt) Pipe Maze**



  Again difficult part2. I solved it using [PNPOLY](https://wrfranklin.org/Research/Short_Notes/pnpoly.html) a super

  handy (and short) point inside polygon check algorithm.



- **[Day 12:](src/main/kotlin/y2023/day12/Day12.kt) Hot Springs**



  I struggled a lot with part2. After reading a few tips and discussions on that puzzle, I solved it eventually using a

  [memoized](https://en.wikipedia.org/wiki/Memoization) recursion (what seems to be a common technique but was completely new to me).



- **Day 14: Parabolic Reflector Dish**



  This was a fun one! For part 1 I have an [alternative solution](src/main/kotlin/y2023/day14/Day14Kool.kt), which solves

  the puzzle using physics simulation including fancy 3D graphics. Also runs in the

  [browser](https://fabmax.github.io/kool/aoc23-day14/) I used [kool](https://github.com/fabmax/kool) for 

  that, my own kotlin 3D game engine :smile:



  For my [regular solution](src/main/kotlin/y2023/day14/Day14.kt) I went for speed instead of elegance: After a few

  warmup-iterations, the part 2 result completes in under 10 ms (Java 21, Ryzen 7950X, Ubuntu).



- **[Day 19:](src/main/kotlin/y2023/day19/Day19.kt) Aplenty**

 

  Another straight-forward part 1 followed by a pretty difficult part 2. After struggling a bit with range bounds

  it worked out ok. Just for fun, I also implemented two rather useless brute force approaches: On

  [CPU](src/main/kotlin/y2023/day19/Day19BruteForce.kt) (estimated time to complete: 2.6 days at 1.13G part checks / second,

  Ryzen 7950X) as well as on [GPU](src/main/kotlin/y2023/day19/Day19Compute.kt) (estimated time to complete: 1h:34m at 45.1G part checks / second, RTX4080, Windows).



- **[Day 21:](src/main/kotlin/y2023/day21/Day21.kt) Step Counter**

 

  Wow, that was a tough one. In the end my solution is pretty straight forward, but getting there was rough...



- **[Day 22:](src/main/kotlin/y2023/day22/Day22.kt) Sand Slabs**



  Not too special, but there's another nice visualization for the brick stack.



- **[Day 24:](src/main/kotlin/y2023/day24/Day24.kt) Never Tell Me The Odds**



  Very hard part2. Solved it by approximating the collision times of two hailstones with the rock. Not the most elegant

  solution but I'm happy with it.



- **[Day 25:](src/main/kotlin/y2023/day25/Day25.kt) Snowverload**



  Last one! Find critical edges in a graph. Solved it by finding paths between random nodes and counting the edge

  occurrences.

 

  

## Running the Puzzles



In order to run the puzzles, you need to place your puzzle input into correctly named `.txt` files in the `inputs/2023/` directory:

The implementation expects the day's puzzle input in a file called `day[xx].txt` where `[xx]` has to be replaced by

the day number (e.g. `day01.txt` for day 1, `day10.txt` for day 10, etc.)



Moreover, test-input can be specified in separate `.txt` files in the same directory: `day01_test.txt` for day 1's

test input and so on. Multiple test inputs for the same day can be given by appending an extra number:

`day02_test1.txt`, `day02_test2.txt`, etc.



Test input files are expected to start with a single line containing the expected results (if already known):

```

test1=?; test2=?; part1=?; part2=?



[test input here]

```

Where the `?` can be replaced with the expected results for part 1 / part 2 (for test input and main puzzle). You can

also keep the `?` or remove the entire entry if the expected result is not yet known. Moreover, if the expected

test result is only specified for a single part, only that part is executed.



## Previous Advents of Code



From time to time I solve puzzles from the previous years. Solutions are located in their individual packages:



- [y2022](src/main/kotlin/y2022): All solutions for year 2022 (50 stars)

- [y2015](src/main/kotlin/y2015): Days 1 to 21 for year 2015 (42 stars so far)