18 lines
684 B
Haskell
18 lines
684 B
Haskell
import qualified Data.Map.Strict as M
|
|
|
|
blinkStone :: (Int, Int) -> [(Int, Int)]
|
|
blinkStone (0, n) = [(1, n)]
|
|
blinkStone (s, n) = let ss = show s
|
|
nDigit = length ss
|
|
in if even nDigit
|
|
then zip (map read [take (nDigit `div` 2) ss, drop (nDigit `div` 2) ss]) [n, n]
|
|
else [(s * 2024, n)]
|
|
|
|
blink :: Int -> M.Map Int Int -> M.Map Int Int
|
|
blink 0 m = m
|
|
blink n m = blink (n - 1) $ M.fromListWith (+) $ concatMap blinkStone $ M.toList m
|
|
|
|
main = do
|
|
contents <- M.fromListWith (+) . flip zip (repeat 1) . map read . words <$> readFile "day11.txt"
|
|
print . M.foldl (+) 0 $ blink 75 contents
|