Haskell

Plenty of scope for making part 2 faster, but I think simple is best here. Forgot to sort the lists in the first part, which pushed me waaay off the leaderboard.

import Data.List

main = do
  [as, bs] <- transpose . map (map read . words) . lines <$> readFile "input01"
  print . sum $ map abs $ zipWith (-) (sort as) (sort bs)
  print . sum $ map (\a -> a * length (filter (== a) bs)) as

Uiua

For entertainment purposes only, I’ll be trying a solution in Uiua each day until it all gets too much for me…

$ 3   4
$ 4   3
$ 2   5
$ 1   3
$ 3   9
$ 3   3
⊜∘⊸≠@\n     # Partition at \n.
⊜(⍆∵⋕)⊸≠@\s # Partition at space, parse ints, sort.

&p/+/(⌵-). # Part1 : Get abs differences, sum, print.

&p/+×⟜(/+⍉≡⌕)°⊂ # Part 2 : Count instances, mul out, sum, print.

Nim

I’ve got my first sub-1000 rank today (998 for part 2). Yay!
Simple and straightforward challenge, very fitting for 1st day. Gonna enjoy it while it lasts.

proc solve(input: string): AOCSolution[int, int] =
  var l1,l2: seq[int]
  for line in input.splitLines():
    let pair = line.splitWhitespace()
    l1.add parseInt(pair[0])
    l2.add parseInt(pair[1])
  l1.sort()
  l2.sort()

  block p1:
    for i in 0..l1.high:
      result.part1 += abs(l1[i] - l2[i])

  block p2:
    for n in l1:
      result.part2 += n * l2.count(n)

Codeberg repo

Rust

Right IDs are directly read into a hash map counter.

use std::str::FromStr;
use std::collections::HashMap;

fn part1(input: String) {
    let mut left = Vec::new();
    let mut right = Vec::new();
    for line in input.lines() {
        let mut parts = line.split_whitespace()
            .map(|p| u32::from_str(p).unwrap());
        left.push(parts.next().unwrap());
        right.push(parts.next().unwrap());
    }
    left.sort_unstable();
    right.sort_unstable();
    let diff: u32 = left.iter().zip(right)
        .map(|(l, r)| l.abs_diff(r))
        .sum();
    println!("{diff}");
}

fn part2(input: String) {
    let mut left = Vec::new();
    let mut right: HashMap<u32, u32> = HashMap::new();
    for line in input.lines() {
        let mut parts = line.split_whitespace()
            .map(|p| u32::from_str(p).unwrap());
        left.push(parts.next().unwrap());
        *right.entry(parts.next().unwrap()).or_default() += 1;
    }
    let similar: u32 = left.iter()
        .map(|n| n * right.get(n).copied().unwrap_or_default())
        .sum();
    println!("{similar}");
}

util::aoc_main!();

TypeScript

import { AdventOfCodeSolutionFunction } from "./solutions";

function InstancesOf(sorted_array: Array<number>, value: number) {
    const index = sorted_array.indexOf(value);
    if(index == -1)
        return 0;

    let sum = 1;

    for (let array_index = index + 1; array_index < sorted_array.length; array_index++) {
        if(sorted_array[array_index] != value)
            break;

        sum += 1;
    }

    return sum;
}

export const solution_1: AdventOfCodeSolutionFunction = (input) => {
    const left: Array<number> = [];
    const right: Array<number> = [];

    const lines = input.split("\n");

    for (let index = 0; index < lines.length; index++) {
        const element = lines[index].trim();
        if(!element)
            continue;

        const leftRight = element.split("   ");
        left.push(Number(leftRight[0]));
        right.push(Number(leftRight[1]));
    }

    const numSort = (a: number, b: number) => a - b;
    left.sort(numSort);
    right.sort(numSort);

    let sum = 0;
    for (let index = 0; index < left.length; index++) {
        const leftValue = left[index];
        const rightValue = right[index];

        sum += Math.abs(leftValue - rightValue);
    }

    const part1 = `Part 1: ${sum}`;

    sum = 0;
    for (let index = 0; index < left.length; index++) {
        sum += left[index] * InstancesOf(right, left[index]);
    }

    const part2 = `Part 2: ${sum}`;

    return `${part1}\n${part2}`;
};

I’m quite inexperienced as a programmer, I learned most of the basic concepts from playing human resource machine and 7 billion humans. After mucking about writing some CLI utilities in Perl and python, I’ve decided to give rust a go.

Part 1

Part 2

Not going to push hard on these first days (fever being a reason), so I slept in quite a bit before looking at the problem.

List<int> _LeftList = new List<int>();
List<int> _RightList = new List<int>();

// Fed via File.ReadLines(...).Select(l => l.Trim())
public void Input(IEnumerable<string> lines)
{
  foreach (var line in lines)
  {
    var split = line.Split(' ', StringSplitOptions.RemoveEmptyEntries).Select(s => int.Parse(s));
    _LeftList.Add(split.First());
    _RightList.Add(split.Last());
  }
}

public void Part1()
{
  Console.WriteLine($"Sum: {_LeftList.Order().Zip(_RightList.Order()).Select(v => Math.Abs(v.First - v.Second)).Sum()}");
}
public void Part2()
{
  Console.WriteLine($"Sum: {_LeftList.Select(l => _RightList.Where(i => i == l).Count() * l).Sum()}");
}

Kotlin

No 💜 for Kotlin here?

import kotlin.math.abs

fun part1(input: String): Int {
    val diffs: MutableList<Int> = mutableListOf()
    val pair = parse(input)
    pair.first.sort()
    pair.second.sort()
    pair.first.forEachIndexed { idx, num ->
        diffs.add(abs(num - pair.second[idx]))
    }
    return diffs.sum()
}

fun part2(input: String): Int {
    val pair = parse(input)
    val frequencies = pair.second.groupingBy { it }.eachCount()
    var score = 0
    pair.first.forEach { num ->
        score += num * frequencies.getOrDefault(num, 0)
    }
    return score
}

private fun parse(input: String): Pair<MutableList<Int>, MutableList<Int>> {
    val left: MutableList<Int> = mutableListOf()
    val right: MutableList<Int> = mutableListOf()
    input.lines().forEach { line ->
        if (line.isNotBlank()) {
            val parts = line.split("\\s+".toRegex())
            left.add(parts[0].toInt())
            right.add(parts[1].toInt())
        }
    }
    return left to right
}

Python

left_list = []
right_list = []

for line in file:
    split_line = line.split()
    left_list.append(int(split_line[0]))
    right_list.append(int(split_line[1]))

sorted_left = sorted(left_list)
sorted_right = sorted(right_list)
distance = []
for left, right in zip(sorted_left, sorted_right):
    distance.append(abs(left - right))

total = sum(distance)

print(total)

file = open('input.txt', 'r')
left_list = []
right_list = []

for line in file:
    split_line = line.split()
    left_list.append(int(split_line[0]))
    right_list.append(int(split_line[1]))

sim_score = 0
for item in left_list:
    sim = right_list.count(item)
    sim_score += (sim * item)

print(sim_score)

I am sure there were better ways to do this, this was just the first way in my head, in the order it appeared

Smalltalk

day1p12: input    
	| list1 list2 nums dist sim |
	
	list1 := OrderedCollection new.
	list2 := OrderedCollection new.
	
	input linesDo: [ :l |
		nums := l substrings collect: [ :n | n asInteger ].
		list1 add: (nums at: 1).
		list2 add: (nums at: 2).
	].

	list1 sort.
	list2 sort.
	
	dist := 0.
	list1 with: list2 do: [ :a :b | dist := dist + (a - b) abs ].
	
	sim := list1 sumNumbers: [ :x | x * (list2 occurrencesOf: x) ].
	
	^ Array with: dist with: sim.

Solution in C

Part 1 is a sort and a quick loop. Part 2 could be efficient with a lookup table but it was practically instant with a simple non-memoized scan so left it that way.

C#

public class Day01 : Solver
{
  private ImmutableArray<int> left;
  private ImmutableArray<int> right;

  public void Presolve(string input)
  {
    var pairs = input.Trim().Split("\n").Select(line => Regex.Split(line, @"\s+"));
    left = pairs.Select(item => int.Parse(item[0])).ToImmutableArray();
    right = pairs.Select(item => int.Parse(item[1])).ToImmutableArray();
  }

  public string SolveFirst() => left.Sort().Zip(right.Sort()).Select((pair) => int.Abs(pair.First - pair.Second)).Sum().ToString();

  public string SolveSecond() => left.Select((number) => number * right.Where(v => v == number).Count()).Sum().ToString();
}

Solution in ruby

This is my third program in ruby after the ruby tutorial and half of the rails tutorial, so don’t expect anything too good from it.

Also i did this today since i had time, i will probably not comment every day.

Rust

I’m doing it in Rust again this year. I stopped keeping up with it after day 3 last year, so let’s hope I last longer this time around.

use std::collections::HashMap;

use crate::utils::read_lines;

pub fn solution1() {
    let (mut id_list1, mut id_list2) = get_id_lists();

    id_list1.sort();
    id_list2.sort();

    let total_distance = id_list1
        .into_iter()
        .zip(id_list2)
        .map(|(left, right)| (left - right).abs())
        .sum::<i32>();

    println!("Total distance = {total_distance}");
}

pub fn solution2() {
    let (id_list1, id_list2) = get_id_lists();

    let id_count_map = id_list2
        .into_iter()
        .fold(HashMap::<_, i32>::new(), |mut map, id| {
            *map.entry(id).or_default() += 1i32;

            map
        });

    let similarity_score = id_list1
        .into_iter()
        .map(|id| id * id_count_map.get(&id).copied().unwrap_or_default())
        .sum::<i32>();

    println!("Similarity score = {similarity_score}");
}

fn get_id_lists() -> (Vec<i32>, Vec<i32>) {
    read_lines("src/day1/input.txt")
        .map(|line| {
            let mut ids = line.split_whitespace().map(|id| {
                id.parse::<i32>()
                    .expect("Ids from input must be valid integers")
            });

            (
                ids.next().expect("First Id on line must be present"),
                ids.next().expect("Second Id on line must be present"),
            )
        })
        .unzip()
}

I’m keeping my solutions up on GitHub.

I’m late to the party, as usual. Damned timezones. This year I’m going to tackle with a small handful of languages, but primarily Elixir and Gleam. This is my first time trying this languages in earnest, so expect some terrible, inefficient and totally unidiomatic code!
Here’s day one:

Elixir

part_one =
  File.read!("input.in")
  |> String.split("\n", trim: true)
  |> Enum.map(fn line ->
    line
    |> String.split()
    |> Enum.map(&String.to_integer/1)
  end)
  |> Enum.reduce({[], []}, fn [first, second], {list1, list2} ->
    {[first | list1], [second | list2]}
  end)
  |> then(fn {list1, list2} ->
    {Enum.sort(list1), Enum.sort(list2)}
  end)
  |> then(fn {list1, list2} ->
    Enum.zip(list1, list2)
    |> Enum.map(fn {x, y} -> abs(x - y) end)
  end)
  |> Enum.sum()

part_two =
  File.read!("input.in")
  |> String.split("\n", trim: true)
  |> Enum.map(fn line ->
    line
    |> String.split()
    |> Enum.map(&String.to_integer/1)
  end)
  |> Enum.reduce({[], []}, fn [first, second], {list1, list2} ->
    {[first | list1], [second | list2]}
  end)
  |> then(fn {list1, list2} ->
    Enum.map(list1, fn line ->
      line * Enum.count(list2, fn x -> x === line end)
    end)
    |> Enum.sum()
  end)

IO.inspect(part_one)
IO.inspect(part_two)