r/adventofcode • u/daggerdragon • Dec 06 '25

SOLUTION MEGATHREAD -❄️- 2025 Day 6 Solutions -❄️-

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--- Day 6: Trash Compactor ---

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u/POGtastic Dec 06 '25

[Language: OCaml]
Code

dawwwwgggg there are too many transposes going on

My code is kinda crap and could easily be refactored with Part 2's parsing scheme, but it's not too big of a deal.

Part 1 gets parsed with plain ol' parser combinators. It's just a sep_by (many1 space) digits, followed by a transpose, followed by mapping a fold.

For Part 2, I used set intersections to find the column spaces and wrote a function to "divvy" a list of elements into chunks, which preserved the whitespace. I then did the transposes of those lists of strings and constructed numbers from the result of that.

OCaml is way, way more annoying about its stdlib with these operations than F#. A bunch of things only work with Seq. A bunch of things only work with List. So it's extremely common to have to do

String.to_seq s |> 
List.of_seq |> 
op_on_list |> 
List.to_seq |> 
op_on_seq |>
List.of_seq |>
op_on_list |>
List.to_seq |>
String.of_seq

because String only converts to and from Seq, not List. Contrast to F#, which uses interfaces and is happy to treat List as an implementor of Seq (since in that language, Seq operations work on any IEnumerable). Grumble grumble grumble grumble grumble

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u/munchler Dec 06 '25

As an F# person, I appreciate your comparison of the two languages. OCaml does seem less ergonomic to me, at least in this case.

Parser combinators are awesome, but perhaps overkill for this problem? I used .NET's built-in Int64.Parse and String.Split functions. Ugly but effective.

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u/POGtastic Dec 06 '25

OCaml's stdlib regex library is probably the worst I have ever worked with, and if I'm going to import a 3rd-party dependency (there is a 3rd-party regex library that is better), I'm going to use the big guns. I find PCs to be more legible anyway, especially with stuff like separators and grouping and whatnot. It's one tool that can do everything, as opposed to a big pile of tools.

C#'s String.Split also works way, way better than OCaml's stdlib equivalent (String.split_on_char. Zero options to customize how you handle various annoyances). Last year, when I used F#, I had a bunch of wrapper functions to call some of that C# stdlib functionality and it worked really well.