Rust

This one wasn’t too bad. The example for part 2 even tells you how to process everything by visiting each card once in order. Another option could be to recursively look at all won copies, but that’s probably much less efficient.

Nim

This one was pretty simple, just parse the numbers into sets and check the size of the intersection. Part 2 just made the scoring mechanism a little more complicated.

• Day 4, part 1
• Day 4, part 2

Haskell

11:39 – I spent most of the time reading the scoring rules and (as usual) writing a parser…

import Control.Monad
import Data.Bifunctor
import Data.List

readCard :: String -> ([Int], [Int])
readCard =
  join bimap (map read) . second tail . break (== "|") . words . tail . dropWhile (/= ':')

countShared = length . uncurry intersect

part1 = sum . map ((\n -> if n > 0 then 2 ^ (n - 1) else 0) . countShared)

part2 = sum . foldr ((\n a -> 1 + sum (take n a) : a) . countShared) []

main = do
  input <- map readCard . lines <$> readFile "input04"
  print $ part1 input
  print $ part2 input

(python) Much easier than day 3.

import pathlib

base_dir = pathlib.Path(__file__).parent
filename = base_dir / "day4_input.txt"

with open(base_dir / filename) as f:
    lines = f.read().splitlines()

score = 0

extra_cards = [0 for _ in lines]
n_cards = [1 for _ in lines]

for i, line in enumerate(lines):
    _, numbers = line.split(":")
    winning, have = numbers.split(" | ")

    winning_numbers = {int(n) for n in winning.split()}
    have_numbers = {int(n) for n in have.split()}

    have_winning_numbers = winning_numbers & have_numbers
    n_matches = len(have_winning_numbers)

    if n_matches:
        score += 2 ** (n_matches - 1)

    j = i + 1
    for _ in range(n_matches):
        if j >= len(lines):
            break
        n_cards[j] += n_cards[i]
        j += 1

answer_p1 = score
print(f"{answer_p1=}")

answer_p2 = sum(n_cards)
print(f"{answer_p2=}")

Ruby

!ruby@programming.dev

Somehow took way longer on the second part than the first part trying a recursive approach and then realizing that was dumb.

https://github.com/snowe2010/advent-of-code/blob/master/ruby_aoc/2023/day04/day04.rb

Python

Questions and feedback welcome!

import collections
import re

from .solver import Solver

class Day04(Solver):
  def __init__(self):
    super().__init__(4)
    self.cards = []

  def presolve(self, input: str):
    lines = input.rstrip().split('\n')
    self.cards = []
    for line in lines:
      left, right = re.split(r' +\| +', re.split(': +', line)[1])
      left, right = map(int, re.split(' +', left)), map(int, re.split(' +', right))
      self.cards.append((list(left), list(right)))

  def solve_first_star(self):
    points = 0
    for winning, having in self.cards:
      matches = len(set(winning) & set(having))
      if not matches:
        continue
      points += 1 << (matches - 1)
    return points

  def solve_second_star(self):
    factors = collections.defaultdict(lambda: 1)
    count = 0
    for i, (winning, having) in enumerate(self.cards):
      count += factors[i]
      matches = len(set(winning) & set(having))
      if not matches:
        continue
      for j in range(i + 1, i + 1 + matches):
        factors[j] = factors[j] + factors[i]
    return count

LANGUAGE: Nim

Welcome to the advent of parsing!
Took me a lot more time than it should (Please, don’t check prior commits 😅).

day_04.nim

Factor on github (with comments and imports):

: line>cards ( line -- winning-nums player-nums )
  ":|" split rest
  [
    [ CHAR: space = ] trim
    split-words harvest [ string>number ] map
  ] map first2
;

: points ( winning-nums player-nums -- n )
  intersect length
  dup 0 > [ 1 - 2^ ] when
;

: part1 ( -- )
  "vocab:aoc-2023/day04/input.txt" utf8 file-lines
  [ line>cards points ] map-sum .
;

: follow-card ( i commons -- n )
  [ 1 ] 2dip
  2dup nth swapd
  over + (a..b]
  [ over follow-card ] map-sum
  nip +
;

: part2 ( -- )
  "vocab:aoc-2023/day04/input.txt" utf8 file-lines
  [ line>cards intersect length ] map
  dup length  swap '[ _ follow-card ]
  map-sum .
;

Nice and easy.

-- SPDX-FileCopyrightText: 2023 Jummit
--
-- SPDX-License-Identifier: GPL-3.0-or-later

local function nums(str)
	local res = {}
	for num in str:gmatch("%d+") do
		res[num] = true
	end
	return res
end

local cards = {}
local points = 0
for line in io.open("4.input"):lines() do
	local winning, have = line:match("Card%s*%d+: (.*) | (.*)")
	winning = nums(winning)
	have = nums(have)
	local first = true
	local score = 0
	local matching = 0
	for num in pairs(have) do
		if winning[num] then
			matching = matching + 1
			if first then
				first = false
				score = score + 1
			else
				score = score * 2
			end
		end
	end
	points = points + score
	table.insert(cards, {have=have, wins=matching, count=1})
end
print(points)

local cardSum = 0
for i, card in ipairs(cards) do
	cardSum = cardSum + card.count
	for n = i + 1, i + card.wins do
		cards[n].count = cards[n].count + card.count
	end
end
print(cardSum)

Feels like the challenges are getting easier than harder currently. Fairly straightforward when doing it the lazy way with python.

import re

winning_number_pattern: re.Pattern = re.compile(r' +([\d ]*?) +\|')
lottery_number_pattern: re.Pattern = re.compile(r'\| +([\d ]*)')


def get_winning_numbers(line: str) -> set[str]:
    return set(winning_number_pattern.search(line).group(1).split())


def get_lottery_numbers(line: str) -> set[str]:
    return set(lottery_number_pattern.search(line).group(1).split())


def get_winnings(winning_numbers: set[str], lottery_numbers: set[str]) -> int:
    return int(2 ** (len(winning_numbers.intersection(lottery_numbers)) - 1))


def puzzle_1() -> int:
    points: int = 0
    with open('day4_scratchcards.txt', 'r', encoding='utf-8') as file:
        for line in file:
            points += get_winnings(get_winning_numbers(line), get_lottery_numbers(line))
    return points


class ScratchCard:
    def __init__(self, line: str):
        self.amount: int = 1
        self.winnings: int = len(get_winning_numbers(line).intersection(get_lottery_numbers(line)))

    def update(self, extra: int) -> None:
        self.amount = self.amount + extra

    def __radd__(self, other):
        return self.amount + other


def puzzle_2() -> int:
    scratch_card_list: list[ScratchCard] = []
    with open('day4_scratchcards.txt', 'r', encoding='utf-8') as file:
        for line in file:
            scratch_card_list.append(ScratchCard(line))

    for i, scratch_card in enumerate(scratch_card_list):
        for j in range(1, scratch_card.winnings + 1):
            try:
                scratch_card_list[i + j].update(scratch_card.amount)
            except IndexError:
                pass
    return sum(scratch_card_list)


if __name__ == '__main__':
    print(puzzle_1())
    print(puzzle_2())

Language: C

Another day of parsing, another day of strsep() to the rescue. Today was one of those satisfying days where the puzzle text is complicated but the solution is simple once well understood.

GitHub link

int main()
{
	char line[128], *rest, *tok;
	int nextra[200]={0}, nums[10], nnums;
	int p1=0,p2=0, id,val,nmatch, i;

	for (id=0; (rest = fgets(line, sizeof(line), stdin)); id++) {
		nnums = nmatch = 0;

		while ((tok = strsep(&rest, " ")) && !strchr(tok, ':'))
			;
		while ((tok = strsep(&rest, " ")) && !strchr(tok, '|'))
			if ((val = atoi(tok)))
				nums[nnums++] = val;
		while ((tok = strsep(&rest, " ")))
			if ((val = atoi(tok)))
				for (i=0; i

APL

I’m using this years’ AoC to learn (Dyalog) APL, so this is probably terrible code. I’m happy to receive pointers for improvement, particularly if there is a way to write the same logic with tacit functions or inner/outer products that I missed.

input←⊃⎕NGET'inputs/day4.txt'1
num_matches←'Card [ \d]+: ([ 0-9]+) \| ([ 0-9]+)'⎕S{≢↑∩/0~⍨¨{,⎕CSV⍠'Separator' ' '⊢⍵'S'3}¨⍵.(1↓Lengths↑¨Offsets↓¨⊂Block)} input
⎕←+/2*1-⍨0~⍨num_matches ⍝ part 1
⎕←+/{⍺←0 ⋄ ⍺=≢⍵:⍵ ⋄ (⍺+1)∇⍵ + (≢⍵)↑∊((⍺+1)⍴0)(num_matches[⍺]⍴⍵[⍺])((≢⍵)⍴0)}(≢num_matches)⍴1 ⍝ part 2

Language: Python

Numbers = set[int]
Card    = list[Numbers]

def read_cards(stream=sys.stdin) -> Iterator[Card]:
    for line in stream:
        yield [set(map(int, n.split())) for n in line.split(':')[-1].split('|')]

def main(stream=sys.stdin) -> None:
    cards  = [numbers & winning for winning, numbers in read_cards(stream)]
    points = sum(2**(len(card)-1) for card in cards if card)
    print(points)

def main(stream=sys.stdin) -> None:
    cards  = [numbers & winning for winning, numbers in read_cards(stream)]
    counts = defaultdict(int)

    for index, card in enumerate(cards, 1):
        counts[index] += 1
        for copy in range(index + 1, index + len(card) + 1):
            counts[copy] += counts[index]

    print(sum(counts.values()))

GitHub Repo

PHP

Today was the easiest day so far IMHO. Today, I coded in PHP, a horrible language that produces even worse code. (Ok, full confession, I fed my family for about half a decade on PHP. I seemed to have gotten stuck with it, and so I earned a PhD to escape it.)

Anyway, the only trouble I had was I forgot about the explode function’s capacity to return empty strings. Once I filtered those I had the correct answer on the first one, and then 10 minutes later I had the second part. I wrote my code true to raw php’s awful idioms, though I didn’t make it web based. I read from stdin.

My code is linked on github:

• https://github.com/pngwen/advent-2023/blob/main/day-4a.php
• https://github.com/pngwen/advent-2023/blob/main/day-4b.php

I enjoyed this one. It was a nice simple break after Days 1 and 3; the type of basic puzzle I expect from the first few days of Advent of Code. Pretty simple logic in this one, I don’t think I would change too much. I’m sure I’ll find a way to clean up how it’s written a bit, but I’m happy with this one today.

https://github.com/capitalpb/advent_of_code_2023/blob/main/src/solvers/day04.rs

struct Scratchcard {
    winning_numbers: HashSet,
    player_numbers: HashSet,
}

impl Scratchcard {
    fn from(input: &str) -> Scratchcard {
        let (_, numbers) = input.split_once(':').unwrap();
        let (winning_numbers, player_numbers) = numbers.split_once('|').unwrap();
        let winning_numbers = winning_numbers
            .split_ascii_whitespace()
            .filter_map(|number| number.parse::().ok())
            .collect::>();
        let player_numbers = player_numbers
            .split_ascii_whitespace()
            .filter_map(|number| number.parse::().ok())
            .collect::>();

        Scratchcard {
            winning_numbers,
            player_numbers,
        }
    }

    fn matches(&self) -> u32 {
        self.winning_numbers
            .intersection(&self.player_numbers)
            .count() as u32
    }
}

pub struct Day04;

impl Solver for Day04 {
    fn star_one(&self, input: &str) -> String {
        input
            .lines()
            .map(Scratchcard::from)
            .map(|card| {
                let matches = card.matches();
                if matches == 0 {
                    0
                } else {
                    2u32.pow(matches - 1)
                }
            })
            .sum::()
            .to_string()
    }

    fn star_two(&self, input: &str) -> String {
        let cards: Vec = input.lines().map(Scratchcard::from).collect();
        let mut card_counts = vec![1usize; cards.len()];

        for card_number in 0..cards.len() {
            let matches = cards[card_number].matches();

            if matches == 0 {
                continue;
            }

            for i in 1..=matches {
                card_counts[card_number + i as usize] += card_counts[card_number];
            }
        }

        card_counts.iter().sum::().to_string()
    }
}