Scheme/Guile

Guile doesn't seem to come with a bag implementation :(. Not a big deal, a linear scan works about as well.

(use-modules (ice-9 rdelim))
(use-modules (srfi srfi-1))

(define (parse-file file-name)
  (let* ((p (open-input-file file-name))
        (comma-split (string-split (read-line p) #\,))
        (number-list (map string->number comma-split)))
    number-list))

(let* ((crates (parse-file "notes/everybody_codes_e2025_q03_p1.txt"))
       (dedup-crates (delete-duplicates crates)))
  (format #t "P1 Answer: ~a\n\n" (apply + dedup-crates)))


(let* ((crates (parse-file "notes/everybody_codes_e2025_q03_p2.txt"))
       (dedup-crates (delete-duplicates crates))
       (sorted-crates (sort dedup-crates <)))
  (format #t "P2 Answer: ~a\n\n" (apply + (take sorted-crates 20))))


(let* ((crates (parse-file "notes/everybody_codes_e2025_q03_p3.txt"))
       (sorted-crates (sort crates <))
       (largest-set-size (let loop ((count 0) (l sorted-crates) (c #f) (max-count 0))
         (if (nil? l)
             max-count
             (let* ((new-c (car l))
                    (new-count (if (equal? new-c c) (+ count 1) 1)))
               (loop new-count (cdr l) new-c (max new-count max-count)))))))
  (format #t "P3 Answer: ~a\n\n" largest-set-size))

yeah that must have been confusing 😂

Thank you for this update. Now that problwm and solution fit, I can understand whats going on in your code :]

I was stuck for a while on part 2. I thought I was running into precision errors, so I re-implemented everything using exact integers, then I re-implemented it in python, but it turns out that I just had an off-by-1 error. It just so happened that my off-by-1 algorithm gave the correct solution to the sample input. Part 3 takes a while to compute.

Scheme/Guile

(use-modules (ice-9 rdelim))
(use-modules (ice-9 format))
(use-modules (srfi srfi-1))

(define (parse-file file-name)
  (let* ((p (open-input-file file-name))
        (equality-split (string-split (read-line p) #\=))
        (complex-str (list-ref equality-split 1))
        (complex-parts (map string->number (string-split
          (substring/read-only complex-str 1 (- (string-length complex-str) 1))
          #\,))))
    (+ (car complex-parts) (* 0+1i (list-ref complex-parts 1)))))
(define (special-div numerator divisor)
  (+
    (truncate/ (real-part numerator) (real-part divisor))
    (* 0+1i (truncate/ (imag-part numerator) (imag-part divisor)))))

(let* ((A (parse-file "notes/everybody_codes_e2025_q02_p1.txt")))
  (format #t "Input is ~a\n" A)
  (let loop ((R 0+0i) (i 3))
    (if (> i 0)
      (loop (+ (special-div (* R R) 10+10i) A) (- i 1))
      (format #t "P1 Answer: [~d,~a]\n\n"
              (inexact->exact (real-part R))
              (inexact->exact (imag-part R))))))


(define (check-engrave-range value)
  (and-map (lambda (x) (<= (abs x) 1000000)) (list (real-part value) (imag-part value))))
(define (check-engrave point)
  (let loop ((result 0+0i) (i 100))
    (if (and (> i 0) (check-engrave-range result))
      (loop (+ point (special-div (* result result) 100000+100000i)) (- i 1))
      (check-engrave-range result))))
(let* ((origin (parse-file "notes/everybody_codes_e2025_q02_p2.txt"))
       (engrave-count 0))
  (format #t "Input is ~a\n" origin)
  (let loop ((i 0))
    (if (<= i 1000) (begin
      (let loop ((j 0))
        (if (<= j 1000) (begin
          (set! engrave-count (+ engrave-count
                                 (if (check-engrave (+ origin (+ i (* j 0+1i)))) 1 0)))
          (loop (+ j 10)))))
      (loop (+ i 10)))))
  (format #t "P2 answer: ~a\n\n" engrave-count))


(let* ((origin (parse-file "notes/everybody_codes_e2025_q02_p3.txt"))
       (engrave-count 0))
  (format #t "Input is ~a\n" origin)
  (let loop ((i 0))
    (if (<= i 1000) (begin
      (let loop ((j 0))
        (if (<= j 1000) (begin
          (set! engrave-count
                (+ engrave-count (if (check-engrave (+ origin (+ i (* j 0+1i)))) 1 0)))
          (loop (+ j 1)))))
      (loop (+ i 1)))))
  (format #t "P3 answer: ~a\n\n" engrave-count))

I forgot that "weekdays" for a US website means something different for me here in UTC+9.

This was surprisingly fiddly, but I think I managed to do it reasonably neatly.

import Control.Arrow  
import Data.Foldable  
import Data.List (sortBy)  
import Data.List.Split  
import Data.Maybe  
import Data.Ord  

data Fishbone  
  = Fishbone (Maybe Int) Int (Maybe Int) Fishbone  
  | Empty  
  deriving (Eq)  

instance Ord Fishbone where  
  compare = comparing numbers  

readInput :: String -> [(Int, Fishbone)]  
readInput = map readSword . lines  
  where  
    readSword = (read *** build) . break (== ':')  
    build = foldl' insert Empty . map read . splitOn "," . tail  

insert bone x =  
  case bone of  
    (Fishbone l c r next)  
      | isNothing l && x < c -> Fishbone (Just x) c r next  
      | isNothing r && x > c -> Fishbone l c (Just x) next  
      | otherwise -> Fishbone l c r $ insert next x  
    Empty -> Fishbone Nothing x Nothing Empty  

spine (Fishbone _ c _ next) = c : spine next  
spine Empty = []  

numbers :: Fishbone -> [Int]  
numbers (Fishbone l c r next) =  
  (read $ concatMap show $ catMaybes [l, Just c, r])  
    : numbers next  
numbers Empty = []  

quality :: Fishbone -> Int  
quality = read . concatMap show . spine  

part1, part2, part3 :: [(Int, Fishbone)] -> Int  
part1 = quality . snd . head  
part2 = uncurry (-) . (maximum &&& minimum) . map (quality . snd)  
part3 = sum . zipWith (*) [1 ..] . map fst . sortBy (flip compareSwords)  
  where  
    compareSwords =  
      comparing (quality . snd)  
        <> comparing snd  
        <> comparing fst  

main =  
  forM_  
    [ ("everybody_codes_e2025_q05_p1.txt", part1),  
      ("everybody_codes_e2025_q05_p2.txt", part2),  
      ("everybody_codes_e2025_q05_p3.txt", part3)  
    ]  
    $ \(input, solve) -> readFile input >>= print . solve . readInput  

I liked this one!

import Control.Arrow  
import Control.Monad  
import Data.List  
import Data.Ratio  

simpleTrain = uncurry (%) . (head &&& last) . map read  

compoundTrain input =  
  let a = read $ head input  
      z = read $ last input  
      gs =  
        map  
          ( uncurry (%)  
              . (read *** read . tail)  
              . break (== '|')  
          )  
          $ (tail . init) input  
   in foldl' (/) (a % z) gs  

part1, part2, part3 :: [String] -> Integer  
part1 = floor . (2025 *) . simpleTrain  
part2 = ceiling . (10000000000000 /) . simpleTrain  
part3 = floor . (100 *) . compoundTrain  

main =  
  forM_  
    [ ("everybody_codes_e2025_q04_p1.txt", part1),  
      ("everybody_codes_e2025_q04_p2.txt", part2),  
      ("everybody_codes_e2025_q04_p3.txt", part3)  
    ]  
    $ \(input, solve) -> readFile input >>= print . solve . lines  

I thought this was going to be the knapsack problem, but no.

import Control.Monad  
import Data.List.Split  
import qualified Data.Set as Set  
import qualified Data.Multiset as MSet  

part1, part2, part3 :: [Int] -> Int  
part1 = sum . Set.fromList  
part2 = sum . Set.take 20 . Set.fromList  
part3 = maximum . MSet.toCountMap . MSet.fromList  

main =  
  forM_  
    [ ("everybody_codes_e2025_q03_p1.txt", part1),  
      ("everybody_codes_e2025_q03_p2.txt", part2),  
      ("everybody_codes_e2025_q03_p3.txt", part3)  
    ]  
    $ \(input, solve) ->  
      readFile input >>= print . solve . map read . splitOn ","  

I was scared of a hard combinatorial puzzle day, but this was a breeze.

{-# LANGUAGE TupleSections #-}
module Main (main) where
import Control.Monad ((<$!>))
import qualified Data.Text.IO as TextIO
import Data.Text (Text)
import qualified Data.Text as Text
import qualified Data.IntSet as IntSet
import Control.Arrow ((>>>))
import qualified Data.List as List
import qualified Data.IntMap as IntMap

part1 :: [IntSet.Key] -> IntSet.Key
part1 = IntSet.fromList
  >>> IntSet.foldl (+) 0

part2 :: [IntSet.Key] -> IntSet.Key
part2 = IntSet.fromList
  >>> IntSet.toAscList
  >>> take 20
  >>> sum

part3 :: [IntMap.Key] -> Int
part3 = List.map (, 1)
  >>> IntMap.fromListWith (+)
  >>> IntMap.toList
  >>> List.map snd
  >>> maximum

main :: IO ()
main = do
  sizes <- map (read . Text.unpack) . Text.split (== ',') <$!> TextIO.getLine
  print $ part1 sizes
  print $ part2 sizes
  print $ part3 sizes

I'm still learning Scheme, but I wrote a solution in Guile:

(use-modules (ice-9 rdelim ))
(use-modules (srfi srfi-1))

(define (parse-step s) (*
    (if (eq? (string-ref s 0) #\L) -1 1)
    (string->number (substring s 1))
))
(define (parse-file file-name) (begin
  (define p (open-input-file file-name))
  (define names-str (read-line p))
  (read-line p)
  (define steps-str (read-line p))
  (cons
    (string-split names-str #\,)
    (map parse-step (string-split steps-str #\,))
  )
))

(let* ((parsed-file (parse-file "notes/everybody_codes_e2025_q01_p1.txt"))
       (names (car parsed-file))
       (steps (cdr parsed-file)))
  (format #t "names: ~a\nsteps: ~a\n" names steps)
  (define name-count (length names))
  (define chosen-name-idx (reduce
    (lambda (pos change) (max 0 (min (- name-count 1) (+ pos change))))
    0 steps))
  (format #t "P1: Chosen name(~a): ~a\n\n" chosen-name-idx (list-ref names chosen-name-idx))
)

(let* ((parsed-file (parse-file "notes/everybody_codes_e2025_q01_p2.txt"))
       (names (car parsed-file))
       (steps (cdr parsed-file)))
  (format #t "names: ~a\nsteps: ~a\n" names steps)
  (define name-count (length names))
  (define chosen-name-idx (modulo (reduce + 0 steps) name-count))
  (format #t "P2: Chosen name(~a): ~a\n\n" chosen-name-idx (list-ref names chosen-name-idx))
)

(let* ((parsed-file (parse-file "notes/everybody_codes_e2025_q01_p3.txt"))
       (names (list->vector (car parsed-file)))
       (steps (cdr parsed-file)))
  (format #t "names: ~a\nsteps: ~a\n" names steps)
  (define name-count (vector-length names))
  (for-each (lambda (s)
      (define head (vector-ref names 0))
      (define swap-pos (modulo s name-count))
      (vector-set! names 0 (vector-ref names swap-pos))
      (vector-set! names swap-pos head)
    ) steps)
  (format #t "P3: Chosen name: ~a\n" (vector-ref names 0))
)

I struggled for a long time because I had nearly the correct results. I had to switch div with quot.

This puzzle was fun. If you have a visualization, it's even cooler. (It's a fractal)

{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE PatternSynonyms #-}
{-# OPTIONS_GHC -Wall #-}
module Main (main) where
import Text.Read (ReadPrec, Read (readPrec))
import Data.Functor ((<&>))
import Data.Text (pattern (:<), Text)
import qualified Data.Text as Text
import qualified Data.Text.IO as TextIO
import Control.Monad ((<$!>))
import Control.Arrow ((<<<))

newtype Complex = Complex (Int, Int)

instance Read Complex where
  readPrec :: ReadPrec Complex
  readPrec = readPrec <&> \case
    [a, b] -> Complex (a, b)
    _ -> undefined

instance Show Complex where
  show :: Complex -> String
  show (Complex (a, b))= show [a, b]

readAEquals :: Text -> Complex
readAEquals ('A' :< '=':< rest) = read $ Text.unpack rest
readAEquals _ = undefined


-- >>> Complex (1, 1) `add` Complex (2, 2)
-- [3,3]

add :: Complex -> Complex -> Complex
(Complex (x1, y1)) `add` (Complex (x2, y2)) = Complex (x1 + x2, y1 + y2)

-- >>> Complex (2, 5) `times` Complex (5, 7)
-- [-25,-11]

times :: Complex -> Complex -> Complex
(Complex (x1, y1)) `times` (Complex (x2, y2)) = Complex (x1 * x2 - y1 * y2, x1 * y2 + x2 * y1)

dividedBy :: Complex -> Complex -> Complex
(Complex (x1, y1)) `dividedBy` (Complex (x2, y2)) = Complex (x1 `quot` x2, y1 `quot` y2)

step :: Complex -> Complex -> Complex
step a r = let
 r1 = r `times` r
 r2 = r1 `dividedBy` Complex (10, 10)
 r3 = r2 `add` a
 in r3

zero :: Complex
zero = Complex (0, 0)

part1 :: Complex -> Complex
part1 a = iterate (step a) (Complex (0, 0)) !! 3

shouldBeEngraved :: Complex -> Bool
shouldBeEngraved complexPoint = let

  cycleStep :: Complex -> Complex -> Complex
  cycleStep point r = let
    r2 = r `times` r
    r3 = r2 `dividedBy` Complex (100000, 100000)
    in point `add` r3

  inRange x = x <= 1000000 && x >= -1000000


  in all (\ (Complex (x, y)) -> inRange x && inRange y)
    <<< take 101
    <<< iterate (cycleStep complexPoint)
    $ zero

-- >>> shouldBeEngraved $ Complex (35630,-64880)
-- True
-- >>> shouldBeEngraved $ Complex (35460, -64910)
-- False
-- >>> shouldBeEngraved $ Complex (35630, -64830)
-- False

part2 :: Complex -> Int
part2 (Complex (xA, yA)) = let

    xB = xA + 1000
    yB = yA + 1000

  in length . filter shouldBeEngraved $ do
    x <- [xA, xA+10.. xB]
    y <- [yA, yA+10.. yB]
    pure $ Complex (x, y)

part3 :: Complex -> Int
part3 (Complex (xA, yA)) = length . filter shouldBeEngraved $ do
  x <- [xA..xA+1000]
  y <- [yA..yA+1000]
  pure $ Complex (x, y)

-- >>> [0, 10..100]
-- [0,10,20,30,40,50,60,70,80,90,100]

main :: IO ()
main = do
  a <- readAEquals <$!> TextIO.getContents
  print $ part1 a
  print $ part2 a
  print $ part3 a

My girlfriend is learning python, we are taking on the challenges together, today I may upload her solution:

A=[-3344,68783]
R = [0, 0]
B= [A[0]+1000, A[1]+1000]
pointsengraved = 0
cycleright = 0


for i in range(A[1], B[1]+1):
    for j in range(A[0], B[0]+1):
        for k in range(100):
            R = [int(R[0] * R[0] - R[1] * R[1]), int(R[0] * R[1] + R[1] * R[0])]
            R = [int(R[0] / 100000), int(R[1] / 100000)]
            R = [int(R[0] + j), int(R[1] + i)]
            if -1000000>R[0] or R[0]>1000000 or -1000000>R[1] or R[1]>1000000:
                #print(".", end="")
                break
            cycleright += 1
        if cycleright == 100:
            pointsengraved += 1
            #print("+", end="")
        cycleright = 0
        R = [0, 0]
    #print()

print(pointsengraved)

The commented out print statements produce an ascii map of the set, which can be cool to view at the right font size.

Nim

Nothing fancy. Simple iterative tree construction and sort, using the std/algorithm and a custom < operator on types.

type
  LeafNode = ref object
    value: int
  Node = ref object
    value: int
    left, right: LeafNode
    center: Node
  Sword = object
    id, quality: int
    levels: seq[int]
    fishbone: Node

proc add(node: var Node, val: int) =
  var curNode = node
  while not curNode.isNil:
    if val < curNode.value and curNode.left.isNil:
      curNode.left = LeafNode(value: val)
      return
    elif val > curNode.value and curNode.right.isNil:
      curNode.right = LeafNode(value: val)
      return
    elif curNode.center.isNil:
      curNode.center = Node(value: val)
      return
    else: curNode = curNode.center
  node = Node(value: val)

proc calcQuality(sword: Sword): int =
  var res = ""
  var curNode = sword.fishbone
  while not curNode.isNil:
    res &= $curNode.value
    curNode = curNode.center
  return parseInt(res)

proc getLevels(s: Sword): seq[int] =
  var curNode = s.fishbone
  while not curNode.isNil:
    var strVal = ""
    strVal &= (if curNode.left.isNil:  "" else: $curNode.left.value)
    strVal &= $curNode.value
    strVal &= (if curNode.right.isNil: "" else: $curNode.right.value)
    result.add parseInt(strVal)
    curNode = curNode.center

proc `<`(s1, s2: seq[int]): bool =
  for i in 0..min(s1.high, s2.high):
    if s1[i] != s2[i]: return s1[i] < s2[i]
  s1.len < s2.len

proc `<`(s1, s2: Sword): bool =
  if s1.quality != s2.quality: s1.quality < s2.quality
  elif s1.levels != s2.levels: s1.levels < s2.levels
  else: s1.id < s2.id

proc parseSwords(input: string): seq[Sword] =
  for line in input.splitLines:
    let numbers = line.split({':',','}).mapIt(parseInt(it))
    var node= Node(value: numbers[1])
    for num in numbers.toOpenArray(2, numbers.high):
      node.add num
    result &= Sword(id: numbers[0], fishbone: node)

proc solve_part1*(input: string): Solution =
  let swords = parseSwords(input)
  result := swords[0].calcQuality()

proc solve_part2*(input: string): Solution =
  let qualities = parseSwords(input).mapIt(it.calcQuality())
  result := qualities.max - qualities.min

proc solve_part3*(input: string): Solution =
  var swords = parseSwords(input)
  for i in 0..swords.high:
    swords[i].levels = swords[i].getLevels()
    swords[i].quality = swords[i].calcQuality()
  swords.sort(Descending)
  for pos, id in swords.mapit(it.id):
    result.intVal += (pos+1) * id

Full solution at Codeberg: solution.nim

Nim

For part 3 I parse gears as tuples, with regular gears having same value on both ends e.g.

3|5 -> (3, 5)
3   -> (3, 3)

proc parseGears(input: string): seq[int] =
  for line in input.splitLines():
    result.add parseInt(line)

proc parseNestedGears(input: string): seq[(int, int)] =
  for line in input.splitLines():
    let nested = line.split('|').mapIt(it.parseInt)
    result.add:
      if nested.len == 1: (nested[0], nested[0])
      else: (nested[0], nested[1])

proc solve_part1*(input: string): Solution =
  let gears = parseGears(input)
  result := 2025 * gears[0] div gears[^1]

proc solve_part2*(input: string): Solution =
  let gears = parseGears(input)
  result := ceil(10000000000000'f64 / (gears[0] / gears[^1])).int

proc solve_part3*(input: string): Solution =
  let gears = parseNestedGears(input)
  let ratios = (0..gears.high-1).mapIt(gears[it][1] / gears[it+1][0])
  result := int(100 * ratios.prod)

Full solution at Codeberg: solution.nim

Nim

Reading this day's quest I was at first a bit confused what it asks me to calculate. Took me about a minute to realize that most of descriptions are not important and actual calculations for each part are very simple:

part 1 wants sum of each unique crate size
part 2 is same but only 20 smallest
part 3 is max count, because you can always put most crates in one large set and you only need 1 extra set per duplicate crate

proc solve_part1*(input: string): Solution =
  var seen: set[int16]
  for num in input.split(','):
    let num = parseInt(num).int16
    if num in seen: continue
    else:
      seen.incl num
      result.intVal += num

proc solve_part2*(input: string): Solution =
  var set = input.split(',').mapIt(parseInt(it).uint16)
  set.sort()
  result := set.deduplicate(isSorted=true)[0..<20].sum()

proc solve_part3*(input: string): Solution =
  var cnt = input.split(',').toCountTable()
  result := cnt.largest.val

Full solution at Codeberg: solution.nim

Rust

use itertools::Itertools;

type Fishbone = Vec<(i64, Option<i64>, Option<i64>)>;

fn parse_fishbone(quality_str: &str) -> Fishbone {
    let mut fishbone: Fishbone = vec![];
    'outer: for num in quality_str.split(",").map(|x| x.parse().unwrap()) {
        for e in fishbone.iter_mut() {
            if num < e.0 && e.1.is_none() {
                e.1 = Some(num);
                continue 'outer;
            }
            if num > e.0 && e.2.is_none() {
                e.2 = Some(num);
                continue 'outer;
            }
        }
        fishbone.push((num, None, None));
    }
    fishbone
}

fn compute_quality(fishbone: &Fishbone) -> i64 {
    fishbone
        .iter()
        .map(|(c, _, _)| c.to_string())
        .join("")
        .parse()
        .unwrap()
}

pub fn solve_part_1(input: &str) -> String {
    let (_, data) = input.split_once(":").unwrap();
    compute_quality(&parse_fishbone(data)).to_string()
}

pub fn solve_part_2(input: &str) -> String {
    let mut worst_quality = i64::MAX;
    let mut best_quality = i64::MIN;
    for sword in input.lines() {
        let (_, data) = sword.split_once(":").unwrap();
        let quality = compute_quality(&parse_fishbone(data));
        worst_quality = worst_quality.min(quality);
        best_quality = best_quality.max(quality);
    }
    (best_quality - worst_quality).to_string()
}

pub fn solve_part_3(input: &str) -> String {
    let mut swords: Vec<_> = input
        .lines()
        .map(|def| {
            let (id, data) = def.split_once(":").unwrap();
            let fishbone = parse_fishbone(data);
            (id.parse::<i64>().unwrap(), fishbone)
        })
        .collect();
    swords.sort_by(|a, b| {
        let cmp = compute_quality(&a.1).cmp(&compute_quality(&b.1));
        if !matches!(cmp, std::cmp::Ordering::Equal) {
            return cmp;
        }
        for (a_seg, b_seg) in a.1.iter().zip(b.1.iter()) {
            let a_val = match a_seg {
                (a, Some(b), Some(c)) => format!("{b}{a}{c}"),
                (a, Some(b), None) => format!("{b}{a}"),
                (a, None, Some(c)) => format!("{a}{c}"),
                (a, None, None) => format!("{a}"),
            };
            let b_val = match b_seg {
                (a, Some(b), Some(c)) => format!("{b}{a}{c}"),
                (a, Some(b), None) => format!("{b}{a}"),
                (a, None, Some(c)) => format!("{a}{c}"),
                (a, None, None) => format!("{a}"),
            };
            let cmp = a_val.parse::<i64>().unwrap().cmp(&b_val.parse().unwrap());
            if !matches!(cmp, std::cmp::Ordering::Equal) {
                return cmp;
            }
        }
        a.0.cmp(&b.0)
    });
    swords.reverse();
    swords
        .into_iter()
        .enumerate()
        .map(|(pos, (id, _))| id * (pos as i64 + 1))
        .sum::<i64>()
        .to_string()
}

Rust

use num::{BigInt, Integer};

pub fn solve_part_1(input: &str) -> String {
    let gears: Vec<i64> = input.trim().lines().map(|g| g.parse().unwrap()).collect();
    (2025 * gears[0] / gears.last().unwrap()).to_string()
}

pub fn solve_part_2(input: &str) -> String {
    let gears: Vec<i64> = input.trim().lines().map(|g| g.parse().unwrap()).collect();
    let res = (BigInt::parse_bytes(b"10000000000000", 10).unwrap() * gears.last().unwrap())
        .div_ceil(&(BigInt::ZERO + gears[0]));
    res.to_string()
}

pub fn solve_part_3(input: &str) -> String {
    let mut lines = input.trim().lines();
    let first_gear = BigInt::parse_bytes(lines.next().unwrap().as_bytes(), 10).unwrap();
    let mut nominator: BigInt = first_gear * 100;
    let mut denominator: BigInt = BigInt::ZERO + 1;
    for line in lines {
        let mut split = line.split("|");
        denominator *= BigInt::parse_bytes(split.next().unwrap().as_bytes(), 10).unwrap();
        match split.next() {
            Some(size) => {
                nominator *= BigInt::parse_bytes(size.as_bytes(), 10).unwrap();
            }
            None => {
                break;
            }
        }
    }
    (nominator / denominator).to_string()
}

Rust

pub fn solve_part_1(input: &str) -> String {
    let mut crates: Vec<i64> = input.split(",").map(|s| s.parse().unwrap()).collect();
    crates.sort();
    let mut monotonic_subsequence = vec![crates[0]];
    for size in crates.into_iter().skip(1) {
        if size == *monotonic_subsequence.last().unwrap() {
            continue;
        }
        monotonic_subsequence.push(size);
    }
    monotonic_subsequence.iter().sum::<i64>().to_string()
}

pub fn solve_part_2(input: &str) -> String {
    let mut crates: Vec<i64> = input.split(",").map(|s| s.parse().unwrap()).collect();
    crates.sort();
    let mut monotonic_subsequence = vec![crates[0]];
    for size in crates.into_iter().skip(1) {
        if size == *monotonic_subsequence.last().unwrap() {
            continue;
        }
        monotonic_subsequence.push(size);
        if monotonic_subsequence.len() >= 20 {
            break;
        }
    }
    monotonic_subsequence.iter().sum::<i64>().to_string()
}

pub fn solve_part_3(input: &str) -> String {
    let mut crates: Vec<i64> = input.split(",").map(|s| s.parse().unwrap()).collect();
    crates.sort();
    let mut monotonic_subsequences = vec![vec![crates[0]]];
    for size in crates.into_iter().skip(1) {
        let updateable_sequence = monotonic_subsequences
            .iter_mut()
            .find(|v| *v.last().unwrap() < size);
        match updateable_sequence {
            Some(v) => {
                v.push(size);
            }
            None => {
                monotonic_subsequences.push(vec![size]);
            }
        }
    }
    monotonic_subsequences.len().to_string()
}

my boring python solution:

from pathlib import Path


def main():
    input = Path('input.txt').read_text().split('\n')
    names = input[0].split(',')
    instructions = input[-1].split(',')
    print(names,instructions)
    index = 0
    for instruction in instructions:
        dir = instruction[0]
        number = int(instruction[1:])
        if dir == 'L':
            index -= number
            if index < 0:
                index = 0
        else:
            index += number
            if index > len(names) - 1:
                index = len(names) - 1
    print(names[index])
    index = 0
    for instruction in instructions:
        dir = instruction[0]
        number = int(instruction[1:])
        if dir == 'L':
            index -= number
        else:
            index += number
    print(names[index%(len(names))])
    indexes = list(range(len(names)))
    for instruction in instructions:
        dir = instruction[0]
        number = (int(instruction[1:]) if dir == 'R' else -int(instruction[1:])) % len(names)
        indexes[0], indexes[number] = indexes[number], indexes[0]
    print(names[indexes[0]])

if __name__ == "__main__":
    main()

I probably should read all 3 files though. I'll hone it out later.

. means function composition in Haskell. (f .) . (+) is just an obscure way to write \x y -> f (x + y). It's not recommended to use this point-free style in production code, but it is sometimes fun to experiment with for challenges like this.

For quest 2, I decided to implement my own Complex type and operators, because I expected parts 2 and 3 to have something unconventional, but alas it's just a regular Mandelbrot fractal.

Nim again, Nim forever:

type Complex = tuple[x,y: int]
proc `$`(c: Complex): string = &"[{c.x},{c.y}]"
proc `+`(a,b: Complex): Complex = (a.x+b.x, a.y+b.y)
proc `-`(a,b: Complex): Complex = (a.x-b.x, a.y-b.y)
proc `*`(a,b: Complex): Complex = (a.x*b.x - a.y*b.y, a.x*b.y + a.y*b.x)
proc `/`(a,b: Complex): Complex = (a.x div b.x, a.y div b.y)
proc `/`(a: Complex, b: int): Complex = (a.x div b, a.y div b)

proc parseInput(input: string): Complex =
  let parts = input.split({'=','[',',',']'})
  (parseInt(parts[2]), parseInt(parts[3]))

proc isStable(point: Complex, iter: int): bool =
  var num: Complex
  for _ in 1..iter:
    num = (num * num) / 100_000 + point
    if num.x notin -1_000_000 .. 1_000_000 or
       num.y notin -1_000_000 .. 1_000_000:
      return false
  true

proc solve_part1*(input: string): Solution =
  let start = parseInput(input)
  var point: Complex
  for _ in 1..3:
    point = (point * point) / 10 + start
  result := $point

proc solve_part2*(input: string): Solution =
  let start = parseInput(input)
  for y in 0..100:
    for x in 0..100:
      let point: Complex = (start.x + 10 * x, start.y + 10 * y)
      if point.isStable(iter=100): inc result.intVal

proc solve_part3*(input: string): Solution =
  let start = parseInput(input)
  for y in 0..1000:
    for x in 0..1000:
      let point: Complex = (start.x + x, start.y + y)
      if point.isStable(iter=100): inc result.intVal

Full solution at Codeberg: solution.nim

So far I really like the difficulty level of EC, compared to AOC.
Quest 1 is pretty straightforward:

• part 1: add offsets to index then clamp it between 0..limit e.g. min(limit, max(0, index))
• part 2: add offsets and then modulo to figure out last index
• part 3: swap first element with element at index mod names.len until done =)

My solution in Nim:

proc parseInput(input: string): tuple[names: seq[string], values: seq[int]] =
  let lines = input.splitLines()
  result.names = lines[0].split(',')

  let values = lines[2].multiReplace({"R":"","L":"-"})
  for num in values.split(','):
    result.values.add parseInt(num)

proc solve_part1*(input: string): Solution =
  let (names, values) = parseInput(input)
  var pos = 0
  for value in values:
    pos = min(names.high, max(0, pos + value))
  result := names[pos]

proc solve_part2*(input: string): Solution =
  let (names, values) = parseInput(input)
  let pos = values.sum()
  result := names[pos.euclMod(names.len)]

proc solve_part3*(input: string): Solution =
  var (names, values) = parseInput(input)
  for value in values:
    swap(names[0], names[euclMod(value, names.len)])
  result := names[0]

Full solution at Codeberg: solution.nim

Then I forgot which of div and quot I should use, and kept getting nearly the right answer

That sounds amazingly infuriating! and hard to debug. I totally feel you there.

FSharp
(my first submission failed, so I may not be as detailed here)

I laugh at how long this took me. At first I got stuck due to checked arithmetic. In FSharp you open the Checked module and you get the overloaded operators for primitives, whereas CSharp is checked {a + b}. I also mistakenly used distinct on part 3 when I didn't need it.

I did appreciate the choose functions of functional programming, which returns all of the Some values of a sequence of options. The PSeq library let me use 70% of the cpu on the calculations :)

module EveryBodyCodes2025.Quest02  

open System.IO  
open System.Text.RegularExpressions  
open FSharp.Collections.ParallelSeq  
open Checked  

[<Struct>]  
type ComplexNumber = 
    {X: int64; Y: int64}  
    static member (+) (a: ComplexNumber, b: ComplexNumber) = {X = a.X + b.X; Y = a.Y + b.Y }  
    static member (*) (a: ComplexNumber, b: ComplexNumber) = { X = ( a.X * b.X ) - (a.Y * b.Y); Y = (a.X * b.Y) + (a.Y * b.X) }  
    static member (/) (a: ComplexNumber, b: ComplexNumber) = { X = a.X / b.X; Y = a.Y / b.Y }  
    override this.ToString() = $"[{this.X},{this.Y}]"  
    
let parseInput file =  
    File.ReadAllLines file  
    |> fun lines ->  
        let reg = Regex(@"A=\[(-?\d+),(-?\d+)\]")  
        let res = reg.Match(lines[0])  
        match res.Success with  
        | true ->  
            let x = int64 res.Groups[1].Value  
            let y = int64 res.Groups[2].Value  
            {X = x; Y = y}  
        | false -> failwith "failed to parse"  
        
    
let part1 () =  
    parseInput "Inputs/Quest02/Q02_P01.txt"  
    |> fun a ->  
        [1..3]  
        |> List.fold (fun acc _ -> (acc * acc) / { X = 10; Y = 10 } + a ) {X = 0; Y = 0}  

let cycle p =  
    let rec iterate current iteration =  
        if iteration = 100 then Some current  
        else  
            let next = (current * current) / {X = 100_000; Y = 100_000 } + p  
            if abs(next.X) > 1_000_000 || abs(next.Y) > 1_000_000 then  
                None  
            else iterate next (iteration + 1)  
    iterate { X = 0; Y = 0 } 0  

let part2 () =  
    parseInput "Inputs/Quest02/Q02_P02.txt"  
    |> fun a ->  
        seq {  
            for y in 0..100 do  
            for x in 0..100 do  
                yield {X = a.X + (int64 x * 10L); Y = a.Y + (int64 y * 10L)}  
        }  
        |> PSeq.choose cycle  
        |> PSeq.distinct  
        |> PSeq.length  

let part3 () =  
    parseInput "Inputs/Quest02/Q02_P03.txt"  
    |> fun a ->  
        seq {  
            for y in 0..1000 do  
            for x in 0..1000 do  
                yield {X = a.X + (int64 x); Y = a.Y + (int64 y)}  
        }  
        |> PSeq.choose cycle  
        |> PSeq.length  

What do the .s mean in addWith f = (f .) . (+)?

Here's the right challenge. This was a lot simpler than the tracking of cycles.

type Direction = Left | Right  
type Instruction = { Direction: Direction; Distance: int }  
let parseInstruction (segment:string) =  
    let direction = if segment[0] = 'L' then Left else Right  
    let distance = Int32.Parse(segment.AsSpan().Slice(1)) 
    { Direction = direction; Distance = distance }  
    
let inline normalize (array: 'a array) idx =  
    if idx >= 0 then idx % array.Length else array.Length - (-idx % array.Length)  
    
let inline nextIndex instruction idx =  
    match instruction.Direction with  
    | Left -> idx - instruction.Distance  
    | Right -> idx + instruction.Distance  
    
let readFile file =  
    File.ReadAllLines(file)  
    |> fun lines ->  
        let names = lines.[0] |> _.Split(",", StringSplitOptions.RemoveEmptyEntries ||| StringSplitOptions.TrimEntries)  
        let instructions =  
            lines[2]  
            |> _.Split(",", StringSplitOptions.RemoveEmptyEntries ||| StringSplitOptions.TrimEntries)  
            |> Array.map parseInstruction  
        (names, instructions)  

let part1File file : string =  
        readFile file  
        |> fun (names, instructions) ->  
                instructions  
                |> Seq.fold (fun (idx, _) instruction  ->  
                        let next = nextIndex instruction idx |> fun v -> Math.Clamp(v, 0, names.Length - 1)  

                        match Array.tryItem next names with  
                        | Some n -> next, n  
                        | None -> failwith "off array"  
                    ) (0, "")  
        |> snd  
        
let part1 () = part1File "Inputs/Quest01/Q01_P01.txt"  

let part2File file =  
    readFile file  
    |> fun (names, instructions) ->  
        instructions  
        |> Seq.fold (fun (idx, _) instruction ->  
             let next =  nextIndex instruction idx |> normalize names  
             match Array.tryItem next names with  
                        | Some n -> next, n  
                        | None -> failwith "off array"  
                    ) (0, "")  
        |> snd  

let part2() = part2File "Inputs/Quest01/Q01_P02.txt"  

let part3File file =  
    readFile file  
    |> fun (names, instructions) ->  
        // need to preserve a reference to an array that can be mutated  
        let mutable nameArray = names  
        instructions  
        |> Seq.fold (fun _ instruction ->  
            // for this challenge the index doesn't matter  
            let next = match instruction.Direction with  
                        | Left -> names.Length - instruction.Distance  
                        | Right -> instruction.Distance  
                        |> normalize names  
            match Array.tryItem next nameArray with  
                        | Some n ->  
                            nameArray <- arraySwap 0 next names  
                            0, n  
                        | None -> failwith "off array"  
            ) (0, "")  
        |> snd  

let part3() = part3File  "Inputs/Quest01/Q01_P03.txt"  

Hmmm, I am certain I did the wrong one? I did quest 1, I'm pretty sure