Advent of code 2023 (in kotlin)

Solutions to all puzzles of Advent of code 2023

I was awarded "community star" by JetBrains 😄

Results

All solutions work for both parts. There are a few notable days:

• Day 5: 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: Pipe Maze

  Again difficult part2. I solved it using PNPOLY a super handy (and short) point inside polygon check algorithm.

• Day 12: 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 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, which solves the puzzle using physics simulation including fancy 3D graphics. Also runs in the browser I used kool for that, my own kotlin 3D game engine 😄

  For my regular solution 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: 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 (estimated time to complete: 2.6 days at 1.13G part checks / second, Ryzen 7950X) as well as on GPU (estimated time to complete: 1h:34m at 45.1G part checks / second, RTX4080, Windows).

• Day 21: Step Counter

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

• Day 22: Sand Slabs

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

• Day 24: 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: 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: All solutions for year 2022 (50 stars)
• y2015: Days 1 to 21 for year 2015 (42 stars so far)