aoc2020/day1.hs
2020-12-01 20:41:14 +13:00

35 lines
1.0 KiB
Haskell

module Main where
main :: IO ()
main = do
raw <- readFile "day1.txt"
let ls = map read $ lines raw :: [Integer]
in do
case (solveA ls) of
Nothing -> error "no answer"
(Just x) -> putStrLn $ "day1a: " ++ (show x)
case (solveB ls) of
Nothing -> error "no answer"
(Just x) -> putStrLn $ "day1b: " ++ (show x)
solveA :: [Integer] -> Maybe Integer
solveA = solveX (\(x,y) -> x * y)
(\xs -> [ (x,y) | x <- xs
, y <- xs
, x + y == 2020 ])
solveB :: [Integer] -> Maybe Integer
solveB = solveX (\(x,y,z) -> x * y * z)
(\xs -> [ (x,y,z) | x <- xs
, y <- xs
, z <- xs
, x + y + z == 2020 ])
solveX :: Eq a => (a -> Integer) -> ([Integer] -> [a]) -> [Integer] -> Maybe Integer
solveX _ _ [] = Nothing
solveX f g l = if ls == []
then Nothing
else Just $ (f . head) ls
where
ls = g l