Gleam

Struggled with the second part as I am still very new to this very cool language, but got there after scrolling for some inspiration.

import gleam/int
import gleam/io
import gleam/list
import gleam/regex
import gleam/result
import gleam/string
import simplifile

pub fn main() {
  let assert Ok(data) = simplifile.read("input.in")
  part_one(data) |> io.debug
  part_two(data) |> io.debug
}

fn part_one(data) {
  let assert Ok(multiplication_pattern) =
    regex.from_string("mul\\(\\d{1,3},\\d{1,3}\\)")
  let assert Ok(digit_pattern) = regex.from_string("\\d{1,3},\\d{1,3}")
  let multiplications =
    regex.scan(multiplication_pattern, data)
    |> list.flat_map(fn(reg) {
      regex.scan(digit_pattern, reg.content)
      |> list.map(fn(digits) {
        digits.content
        |> string.split(",")
        |> list.map(fn(x) { x |> int.parse |> result.unwrap(0) })
        |> list.reduce(fn(a, b) { a * b })
        |> result.unwrap(0)
      })
    })
    |> list.reduce(fn(a, b) { a + b })
    |> result.unwrap(0)
}

fn part_two(data) {
  let data = "do()" <> string.replace(data, "\n", "") <> "don't()"
  let assert Ok(pattern) = regex.from_string("do\\(\\).*?don't\\(\\)")
  regex.scan(pattern, data)
  |> list.map(fn(input) { input.content |> part_one })
  |> list.reduce(fn(a, b) { a + b })
}

Nim

From a first glance it was obviously a regex problem.
I’m using tinyre here instead of stdlib re library just because I’m more familiar with it.

import pkg/tinyre

proc solve(input: string): AOCSolution[int, int] =
  var allow = true
  for match in input.match(reG"mul\(\d+,\d+\)|do\(\)|don't\(\)"):
    if match == "do()": allow = true
    elif match == "don't()": allow = false
    else:
      let pair = match[4..^2].split(',')
      let mult = pair[0].parseInt * pair[1].parseInt
      result.part1 += mult
      if allow: result.part2 += mult

Codeberg repo

Sorry for the delay posting this one, Ategon seemed to have it covered, so I forgot :D I will do better.

Haskell

Oof, a parsing problem :/ This is some nasty-ass code. step is almost the State monad written out explicitly.

import Control.Monad
import Data.Either
import Data.List
import Text.Parsec

data Ins = Mul !Int !Int | Do | Dont

readInput :: String -> [Ins]
readInput = fromRight undefined . parse input ""
  where
    input = many ins <* many anyChar
    ins =
      choice . map try $
        [ Mul <$> (string "mul(" *> arg) <*> (char ',' *> arg) <* char ')',
          Do <$ string "do()",
          Dont <$ string "don't()",
          anyChar *> ins
        ]
    arg = do
      s <- many1 digit
      guard $ length s <= 3
      return $ read s

run f = snd . foldl' step (True, 0)
  where
    step (e, a) i =
      case i of
        Mul x y -> (e, if f e then a + x * y else a)
        Do -> (True, a)
        Dont -> (False, a)

main = do
  input <- readInput <$> readFile "input03"
  print $ run (const True) input
  print $ run id input

Python

I’m surprised I don’t see more people taking advantage of eval I thought it was pretty slick.

import operator 
import re

with open('input.txt', 'r') as file:
    memory = file.read()

matches = re.findall("mul\(\d{1,3},\d{1,3}\)|don't\(\)|do\(\)", memory)

enabled = 1
filtered_matches = []
for instruction in matches:
    if instruction == "don't()":
        enabled = 0
        continue
    elif instruction == "do()":
        enabled = 1
        continue
    elif enabled: 
        filtered_matches.append(instruction)
multipled = [eval(f"operator.{x}") for x in filtered_matches]
print(sum(multiples))

Rust

use crate::utils::read_lines;

pub fn solution1() {
    let lines = read_lines("src/day3/input.txt");
    let sum = lines
        .map(|line| {
            let mut sum = 0;
            let mut command_bytes = Vec::new();
            for byte in line.bytes() {
                match (byte, command_bytes.as_slice()) {
                    (b')', [.., b'0'..=b'9']) => {
                        handle_mul(&mut command_bytes, &mut sum);
                    }
                    _ if matches_mul(byte, &command_bytes) => {
                        command_bytes.push(byte);
                    }
                    _ => {
                        command_bytes.clear();
                    }
                }
            }

            sum
        })
        .sum::<usize>();

    println!("Sum of multiplication results = {sum}");
}

pub fn solution2() {
    let lines = read_lines("src/day3/input.txt");

    let mut can_mul = true;
    let sum = lines
        .map(|line| {
            let mut sum = 0;
            let mut command_bytes = Vec::new();
            for byte in line.bytes() {
                match (byte, command_bytes.as_slice()) {
                    (b')', [.., b'0'..=b'9']) if can_mul => {
                        handle_mul(&mut command_bytes, &mut sum);
                    }
                    (b')', [b'd', b'o', b'(']) => {
                        can_mul = true;
                        command_bytes.clear();
                    }
                    (b')', [.., b't', b'(']) => {
                        can_mul = false;
                        command_bytes.clear();
                    }
                    _ if matches_do_or_dont(byte, &command_bytes)
                        || matches_mul(byte, &command_bytes) =>
                    {
                        command_bytes.push(byte);
                    }
                    _ => {
                        command_bytes.clear();
                    }
                }
            }

            sum
        })
        .sum::<usize>();

    println!("Sum of enabled multiplication results = {sum}");
}

fn matches_mul(byte: u8, command_bytes: &[u8]) -> bool {
    matches!(
        (byte, command_bytes),
        (b'm', [])
            | (b'u', [.., b'm'])
            | (b'l', [.., b'u'])
            | (b'(', [.., b'l'])
            | (b'0'..=b'9', [.., b'(' | b'0'..=b'9' | b','])
            | (b',', [.., b'0'..=b'9'])
    )
}

fn matches_do_or_dont(byte: u8, command_bytes: &[u8]) -> bool {
    matches!(
        (byte, command_bytes),
        (b'd', [])
            | (b'o', [.., b'd'])
            | (b'n', [.., b'o'])
            | (b'\'', [.., b'n'])
            | (b'(', [.., b'o' | b't'])
            | (b't', [.., b'\''])
    )
}

fn handle_mul(command_bytes: &mut Vec<u8>, sum: &mut usize) {
    let first_num_index = command_bytes
        .iter()
        .position(u8::is_ascii_digit)
        .expect("Guarunteed to be there");
    let comma_index = command_bytes
        .iter()
        .position(|&c| c == b',')
        .expect("Guarunteed to be there.");

    let num1 = bytes_to_num(&command_bytes[first_num_index..comma_index]);
    let num2 = bytes_to_num(&command_bytes[comma_index + 1..]);

    *sum += num1 * num2;
    command_bytes.clear();
}

fn bytes_to_num(bytes: &[u8]) -> usize {
    bytes
        .iter()
        .rev()
        .enumerate()
        .map(|(i, digit)| (*digit - b'0') as usize * 10usize.pow(i as u32))
        .sum::<usize>()
}

Definitely not my prettiest code ever. It would probably look nicer if I used regex or some parsing library, but I took on the self-imposed challenge of not using third party libraries. Also, this is already further than I made it last year!

Kotlin

Just the standard Regex stuff. I found this website to be very helpful to write the patterns. (Very useful in general)

fun main() {
    fun part1(input: List<String>): Int =
        Regex("""mul\(\d+,\d+\)""").findAll(input.joinToString()).sumOf {
            with(Regex("""\d+""").findAll(it.value)) { this.first().value.toInt() * this.last().value.toInt() }
        }

    fun part2(input: List<String>): Int {
        var isMultiplyInstructionEnabled = true  // by default
        return Regex("""mul\(\d+,\d+\)|do\(\)|don't\(\)""").findAll(input.joinToString()).fold(0) { acc, instruction ->
            when (instruction.value) {
                "do()" -> acc.also { isMultiplyInstructionEnabled = true }
                "don't()" -> acc.also { isMultiplyInstructionEnabled = false }
                else -> {
                    if (isMultiplyInstructionEnabled) {
                        acc + with(Regex("""\d+""").findAll(instruction.value)) { this.first().value.toInt() * this.last().value.toInt() }
                    } else acc
                }
            }
        }
    }

    val testInputPart1 = readInput("Day03_test_part1")
    val testInputPart2 = readInput("Day03_test_part2")
    check(part1(testInputPart1) == 161)
    check(part2(testInputPart2) == 48)

    val input = readInput("Day03")
    part1(input).println()
    part2(input).println()
}

´´´

Uiua

Part 1:

&fras "day3/input.txt"
/+≡/×≡⋕≡↘1regex "mul\\((\\d+),(\\d+)\\)"

Part 2:

Filter ← ⍜⊜∘≡⋅""⊸⦷°□
.&fras "day3/input.txt"
∧Filter♭regex"don't\\(\\)?(.*?)(?:do\\(\\)|$)"
/+≡/×≡⋕≡↘1regex "mul\\((\\d+),(\\d+)\\)"

I started poking at doing a proper lexer/parser, but then I thought about how early in AoC it is and how low the chance is that the second part will require proper parsing.

So therefore; hello regex my old friend, I’ve come to talk with you again.

List<string> instructions = new List<string>();

public void Input(IEnumerable<string> lines)
{
  foreach (var line in lines)
    instructions.AddRange(Regex.Matches(line, @"mul\(\d+,\d+\)|do\(\)|don't\(\)").Select(m => m.Value));
}

public void Part1()
{
  var sum = instructions.Select(mul => Regex.Match(mul, @"(\d+),(\d+)").Groups.Values.Skip(1).Select(g => int.Parse(g.Value))).Select(cc => cc.Aggregate(1, (acc, val) => acc * val)).Sum();
  Console.WriteLine($"Sum: {sum}");
}
public void Part2()
{
  bool enabled = true;
  long sum = 0;
  foreach(var inst in instructions)
  {
    if (inst.StartsWith("don't"))
      enabled = false;
    else if (inst.StartsWith("do"))
      enabled = true;
    else if (enabled)
      sum += Regex.Match(inst, @"(\d+),(\d+)").Groups.Values.Skip(1).Select(g => int.Parse(g.Value)).Aggregate(1, (acc, val) => acc * val);
  }
  Console.WriteLine($"Sum: {sum}");
}

Rust with nom parser

Decided to give it a go with the nom parser (first time using this crate). Turned out quite nicely. Had some issues with the alt combinator: All alternatives have to return the same type, using a enum to wrap all options did the trick.

use memmap2::Mmap;
use nom::{
    branch::alt, bytes::complete::*, character::complete::*, combinator::map, multi::many_till,
    sequence::tuple, AsBytes, IResult,
};

#[derive(Debug)]
enum Token {
    Do,
    Dont,
    Mul(u64, u64),
}

fn main() -> anyhow::Result<()> {
    let file = std::fs::File::open("input.txt")?;
    let mmap = unsafe { Mmap::map(&file)? };

    let mut sum_part1 = 0;
    let mut sum_part2 = 0;
    let mut enabled = true;

    let mut cursor = mmap.as_bytes();
    while let Ok(token) = parse(cursor) {
        match token.1 .1 {
            Token::Do => enabled = true,
            Token::Dont => enabled = false,
            Token::Mul(left, right) => {
                let prod = left * right;
                sum_part1 += prod;
                if enabled {
                    sum_part2 += prod;
                }
            }
        }

        cursor = token.0;
    }

    println!("part1: {} part2: {}", sum_part1, sum_part2);

    Ok(())
}

type ParseResult<'a> =
    Result<(&'a [u8], (Vec<char>, Token)), nom::Err<nom::error::Error<&'a [u8]>>>;

fn parse(input: &[u8]) -> ParseResult {
    many_till(
        anychar,
        alt((
            map(doit, |_| Token::Do),
            map(dont, |_| Token::Dont),
            map(mul, |el| Token::Mul(el.2, el.4)),
        )),
    )(input)
}

fn doit(input: &[u8]) -> IResult<&[u8], &[u8]> {
    tag("do()")(input)
}

fn dont(input: &[u8]) -> IResult<&[u8], &[u8]> {
    tag("don't()")(input)
}

type ParsedMulResult<'a> = (&'a [u8], &'a [u8], u64, &'a [u8], u64, &'a [u8]);

fn mul(input: &[u8]) -> IResult<&[u8], ParsedMulResult> {
    tuple((tag("mul"), tag("("), u64, tag(","), u64, tag(")")))(input)
}

Uiua

Uses (abuses?) experimental features of fold to track the running state of do/don’t state. Although it works well and fast, I don’t think I would recommend this code to anyone :-) Try it if you must!

# Experimental!
DataP₁       ← $ xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))
DataP₂       ← $ xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))
GetMul       ← $ mul\((\d{1,3}),(\d{1,3})\)
GetMulDoDont ← $ mul\(\d{1,3},\d{1,3}\)|do\(\)|don\'t\(\)

&p/+≡(/×≡⋕↘1)regex GetMul DataP₁ # Part 1

# Build an accumulator to track running state of do/don't
Filter ← ≡⋕↘1◌∧(⍣("0" °"n"|"1" °"("|.◌)) :"1"∵◇⊡2

regex GetMulDoDont DataP₂
▽⊸≡(¬≍"do()"°□⊢)▽⊸Filter     # Apply Filter, remove the spare 'do's
&p/+≡(/×≡⋕↘1⊢regexGetMul°□⊢) # Get the digits and multiply, sum.

I couldn’t figure it out in haskell, so I went with bash for the first part

Shell

cat example | grep -Eo "mul\([[:digit:]]{1,3},[[:digit:]]{1,3}\)" | cut -d "(" -f 2 | tr -d ")" | tr "," "*" | paste -sd+ | bc

but this wouldn’t rock anymore in the second part, so I had to resort to python for it

Python

import sys

f = "\n".join(sys.stdin.readlines())

f = f.replace("don't()", "\ndon't()\n")
f = f.replace("do()", "\ndo()\n")

import re

enabled = True
muls = []
for line in f.split("\n"):
    if line == "don't()":
        enabled = False
    if line == "do()":
        enabled = True
    if enabled:
        for match in re.finditer(r"mul\((\d{1,3}),(\d{1,3})\)", line):
            muls.append(int(match.group(1)) * int(match.group(2)))
        pass
    pass

print(sum(muls))

Kotlin

fun part1(input: String): Int {
    val pattern = "mul\\((\\d{1,3}),(\\d{1,3})\\)".toRegex()
    var sum = 0
    pattern.findAll(input).forEach { match ->
        val first = match.groups[1]?.value?.toInt()!!
        val second = match.groups[2]?.value?.toInt()!!
        sum += first * second

    }
    return sum
}

fun part2(input: String): Int {
    val pattern = "mul\\((\\d{1,3}),(\\d{1,3})\\)|don't\\(\\)|do\\(\\)".toRegex()
    var sum = 0
    var enabled = true
    pattern.findAll(input).forEach { match ->
        if (match.value == "do()") enabled = true
        else if (match.value == "don't()") enabled = false
        else if (enabled) {
            val first = match.groups[1]?.value?.toInt()!!
            val second = match.groups[2]?.value?.toInt()!!
            sum += first * second
        }
    }
    return sum
}

Rust

Regex made this one pretty straightforward. The second part additionally looks for do() and don't() in the same regex, then we do a case distinction on the match.

use regex::{Regex, Captures};

fn mul_cap(cap: Captures) -> i32 {
    let a = cap.get(1).unwrap().as_str().parse::<i32>().unwrap();
    let b = cap.get(2).unwrap().as_str().parse::<i32>().unwrap();
    a * b
}

fn part1(input: String) {
    let re = Regex::new(r"mul\((\d{1,3}),(\d{1,3})\)").unwrap();
    let res = re.captures_iter(&input).map(mul_cap).sum::<i32>();
    println!("{res}");
}

fn part2(input: String) {
    let re = Regex::new(r"do\(\)|don't\(\)|mul\((\d{1,3}),(\d{1,3})\)").unwrap();
    let mut enabled = true;
    let mut res = 0;
    for cap in re.captures_iter(&input) {
        match cap.get(0).unwrap().as_str() {
            "do()" => enabled = true,
            "don't()" => enabled = false,
            _ if enabled => res += mul_cap(cap),
            _ => {}
        }
    }
    println!("{res}");
}

util::aoc_main!();

C

Yay parsers! I’ve gotten quite comfortable writing these with C. Using out pointers arguments for the cursor that are only updated if the match is successful makes for easy bookkeeping.

#include "common.h"

static int
parse_exact(const char **stringp, const char *expect)
{
	const char *s = *stringp;
	int i;

	for (i=0; s[i] && expect[i] && s[i] == expect[i]; i++)
		;
	if (expect[i])
		return 0;

	*stringp  = &s[i];
	return 1;
}

static int
parse_int(const char **stringp, int *outp)
{
	char *end;
	int val;

	val = (int)strtol(*stringp, &end, 10);
	if (end == *stringp)
		return 0;

	*stringp = end;
	if (outp) *outp = val;
	return 1;
}

static int
parse_mul(const char **stringp, int *ap, int *bp)
{
	const char *cur = *stringp;
	int a,b;

	if (!parse_exact(&cur, "mul(") ||
	    !parse_int(&cur, &a) ||
	    !parse_exact(&cur, ",") ||
	    !parse_int(&cur, &b) ||
	    !parse_exact(&cur, ")"))
		return 0;

	*stringp = cur;
	if (ap) *ap = a;
	if (bp) *bp = b;
	return 1;
}

int
main(int argc, char **argv)
{
	static char buf[32*1024];
	const char *cur;
	size_t nr;
	int p1=0,p2=0, a,b, dont=0;

	if (argc > 1)
		DISCARD(freopen(argv[1], "r", stdin));

	nr = fread(buf, 1, sizeof(buf), stdin);
	assert(!ferror(stdin));
	assert(nr != sizeof(buf));
	buf[nr] = '\0';

	for (cur = buf; *cur; )
		if (parse_exact(&cur, "do()"))
			dont = 0;
		else if (parse_exact(&cur, "don't()"))
			dont = 1;
		else if (parse_mul(&cur, &a, &b)) {
			p1 += a * b;
			if (!dont) p2 += a * b;
		} else
			cur++;

	printf("03: %d %d\n", p1, p2);
}