Day 10 solution

Dependencies

• [2] B527MN66 Solve day 1 for 2020

Change contents

• file addition: day10.hs (----------)
  [2.17]
  + {-# LANGUAGE LambdaCase #-}

  + import Data.List

  + import Data.Maybe

  + import qualified Data.IntMap as IM

  + import System.Environment

  +

  + distribution :: [Int] -> (Int,Int,Int)

  + distribution = foldl' (\(a,b,c) d -> case d of

  + 1 -> let a' = a + 1 in a' `seq` (a',b,c)

  + 2 -> let b' = b + 1 in b' `seq` (a,b',c)

  + 3 -> let c' = c + 1 in c' `seq` (a,b,c')

  + _ -> (a,b,c)

  + ) (0,0,0)

  +

  + differences :: [Int] -> [Int]

  + differences = unfoldr (\case

  + (a:r@(b:_)) -> Just (b - a, r)

  + [_] -> Just (3,[])

  + _ -> Nothing

  + ) . (0:) . sort

  +

  + arrangements :: [Int] -> Integer

  + arrangements l' = snd $ IM.findMax m where

  + l = foldr (\a r -> case r of

  + [] -> [a, a + 3]

  + _ -> a:r

  + ) [] $ sort l'

  + m = IM.insert 0 1 $ IM.fromList $ fmap (\k ->

  + (k, sum $ mapMaybe (\d ->

  + IM.lookup (k - d) m

  + ) [1 .. 3])

  + ) l

  +

  + main = do

  + [fn] <- getArgs

  + jrs <- (map read . words) <$> readFile fn

  + let

  + (s,_,t) = distribution $ differences jrs

  + print $ fromIntegral s * fromIntegral t

  + print $ arrangements jrs

  +