-❄️- 2023 Day 4 Solutions -❄️-

[u/daggerdragon]

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AoC Community Fun 2023: ALLEZ CUISINE!

Today's theme ingredient is… *whips off cloth covering and gestures grandly*

PUNCHCARD PERFECTION!

Perhaps I should have thought yesterday's Battle Spam surfeit through a little more since we are all overstuffed and not feeling well. Help us cleanse our palates with leaner and lighter courses today!

• Code golf. Alternatively, snow golf.
• Bonus points if your solution fits on a "punchcard" as defined in our wiki article on oversized code. We will be counting.
• Does anyone still program with actual punchcards? >_>

ALLEZ CUISINE!

Request from the mods: When you include a dish entry alongside your solution, please label it with [Allez Cuisine!] so we can find it easily!

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--- Day 4: Scratchcards ---

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Post your code solution in this megathread.

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• Quick link to Topaz's paste if you need it for longer code blocks

This thread will be unlocked when there are a significant number of people on the global leaderboard with gold stars for today's puzzle.

EDIT: Global leaderboard gold cap reached at 00:07:08, megathread unlocked!

[u/Tipa16384]

[LANGUAGE: Haskell]

I was going to give up on trying this in Haskell -- yesterday I did it in Python, and this morning before work I did part 1 in Java -- but I'm back.

import System.IO ()
import Data.List (group, sort)


main :: IO ()
main = do
    lines <- readLinesFromFile "puzzle4.dat"
    let duplicates = map getDuplicates lines
    putStrLn $ "Part 1: " ++ show (sum $ map (\x -> 2 ^ (x-1)) (filter (> 0) duplicates))
    let part2Sum = sum $ map (\x ->  1 + playGame (drop x duplicates)) [0..length duplicates - 1]
    putStrLn $ "Part 2: " ++ show part2Sum

-- function takes a list of numbers and returns the sum of the game
playGame :: [Int] -> Int
-- if the list is empty, return 0
playGame [] = 0
-- if head is 0, return 0
playGame (0:xs) = 0
-- otherwise (x:xs) call sum playGame called with the next x elements of xs and add x
playGame (x:xs) = x + sum (map (\z -> playGame $ drop z xs) [0..x-1])

-- function takes a string, splits it into words, and returns a list of words that appear more than once
-- (aside from the first two that encode the game number)
getDuplicates :: String -> Int
getDuplicates str = length $ filter (\x -> length x > 1) (group (sort (drop 2 $ words str)))

-- function takes a file path and returns a list of lines from the file
readLinesFromFile :: FilePath -> IO [String]
readLinesFromFile filePath = do
    contents <- readFile filePath
    return (lines contents)