Regex is doing a lot of the heavy lifting in today's puzzles. That is one of the main reasons why I ended up not using Roc for Advent of Code this year. There is no regex library, and I just couldn't quite wrap my head around the parser combinator library in time for this year. Maybe I'll get around to it next year.
Pattern matching is a powerful tool in general, and really excels at handling the regex matches. I find it a little strange that you can't pattern match in function parameter definitions like you can in most languages with pattern matching. I'm sure there is a good reason for it, but I'm not sure what that is at the moment.
Anyway, here's how I solved today's puzzles:
import gleam/int import gleam/io import gleam/list import gleam/pair import gleam/option.{Some} import gleam/regexp.{Match} import simplifile as file const example1 = " xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5)) " const example2 = " xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5)) " pub fn main() { let assert Ok(input) = file.read("input") let assert 161 = part1(example1) let assert 48 = part2(example2) part1(input) |> int.to_string |> io.println part2(input) |> int.to_string |> io.println } fn mult_pair(x: String, y: String) -> Int { let assert Ok(x) = int.parse(x) let assert Ok(y) = int.parse(y) x * y } fn part1(input: String) -> Int { let assert Ok(re) = regexp.from_string("mul\\((\\d+),(\\d+)\\)") regexp.scan(re, input) |> list.fold(0, fn(sum, match) { let assert Match(_, [Some(x), Some(y)]) = match sum + mult_pair(x, y) }) } fn part2(input: String) -> Int { let assert Ok(re) = regexp.from_string("mul\\((\\d+),(\\d+)\\)|do\\(\\)|don't\\(\\)") regexp.scan(re, input) |> list.fold(#(0, True), fn(state, match) { case match, state { Match(_, [Some(x), Some(y)]), #(sum, True) -> #(sum + mult_pair(x, y), True) Match("do()", _), #(sum, _) -> #(sum, True) Match("don't()", _), #(sum, _) -> #(sum, False) _, _ -> state } }) |> pair.first } 
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