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module Day1
import System
import System.File
import Data.String
import Text.Parser
parsePair : String -> Maybe (Int, Int)
parsePair pair = do
num1 <- parseInteger (fst p1)
num2 <- parseInteger (snd p2)
pure (num1, num2) where
p1 = span (/= ' ') pair
p2 = span (== ' ') (snd p1)
parseStr : String -> List (Int, Int)
parseStr str = do
nums <- lines str
maybe [] pure (parsePair nums)
transposePairs : List (a, b) -> (List a, List b)
transposePairs ls = (map fst ls, map snd ls)
part1 : (List Int, List Int) -> Int
part1 inp = sum $ zipWith (\x => \y => abs (x - y)) (sort $ fst inp) (sort $ snd inp)
occur : Eq a => Num b => a -> List a -> b
occur x fs = foldr (\y => \r => if x == y then r + 1 else r) 0 fs
part2 : (List Int, List Int) -> Int
part2 (l1, l2) = sum $ map (\x => x * (occur x l2)) l1
main : IO ()
main = do
estr <- readFile "data/day1.txt"
str <- either (die . show) pure estr
putStrLn $ show $ part1 $ transposePairs $ parseStr str
putStrLn $ show $ part2 $ transposePairs $ parseStr str
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