aoc2021/Day4_1.hs

module Day4_1 where
import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
import Data.Text (splitOn, unpack, pack)
import Prelude hiding (splitAt)

type Board = [[Int]]

column :: Board -> Int -> [Int]
column board i = map (!! i) board

splitAt :: String -> String -> [String]
splitAt delimiter str = map unpack $ splitOn (pack delimiter) $ pack str

-- remove padding spaces and turn a board line into ints
lineToInts :: String -> [Int]
lineToInts str = map read $ filter (/= "") $ splitAt " " str

isLineWinning :: [Int] -> [Int] -> Bool
isLineWinning nums = all (`elem` nums)

-- in: random numbers, board
-- out: only unmarked numbers in board
unmarkedNums :: [Int] -> Board -> Board
unmarkedNums nums = map (filter (`notElem` nums))

-- in: random numbers, board
-- out: sum of all unmarked numbers
unmarkedSum :: [Int] -> Board -> Int
unmarkedSum nums board = sum . concat $ unmarkedNums nums board

-- in: board, list of random numbers
-- out: true if board won
checkBoard :: Board -> [Int] -> Bool
checkBoard board nums = any (isLineWinning nums) allLines
    where
        allLines = board ++ map (column board) [0..4]

-- in: list of boards, list of random numbers, accumulator
-- out: boards that won, number of iterations
checkBoards' :: [Board] -> [Int] -> [(Board, Int)] -> [(Board, Int)]
checkBoards' [] nums acc = acc
checkBoards' (x:xs) nums acc
    | checkBoard x nums = checkBoards' xs nums (acc ++ [(x, length nums)])
    | otherwise = checkBoards' xs nums acc

-- same thing but checks all possible numbers rather than a single slice of them
checkBoards :: [Board] -> [Int] -> [(Board, Int)]
checkBoards boards nums = filter (\x -> fst x /= []) solutions
    where solutions = [ k |  i <- [1..length nums],
                             let j = take i nums,
                             k <- checkBoards' boards j [] ]

dedup :: Eq a => [(a, b)] -> [(a, b)]
dedup [] = []
dedup (x:xs) = x : dedup (filter (\y -> fst x /= fst y) xs)

main :: IO ()
main = do
    input <- openFile "inputs/4.txt" ReadMode
    contents <- hGetContents input

    -- random numbers from the first line
    let list = map read $ splitAt "," $ head $ splitAt "\n\n" contents :: [Int]
    -- the remaining lines are bingo boards
    let bingus = map lines $ tail $ splitAt "\n\n" contents
    let boards = map (map lineToInts) bingus

    let (board, num) = last . dedup $ checkBoards boards list

    let sum = unmarkedSum (take num list) board 
    print $ sum * list !! (num - 1)

    hClose input