src/advent14/advent14.hs

   1 import qualified Data.Sequence as Q
   2 import Data.Sequence ((<|), (|>))
   3 import Data.List
   4 import Data.Foldable (toList)
   5
   6 type Recipes = Q.Seq Int
   7 data State = State Int Int Recipes deriving (Eq, Show)
   8
   9 targetLength = 327901
  10 -- targetLength = 59414
  11
  12 main :: IO ()
  13 main = do
  14     let state = State 0 1 (Q.fromList [3, 7])
  15     putStrLn $ part1 state
  16     print $ part2 state
  17
  18 part1 :: State -> String
  19 part1 state0 = concatMap show $ toList $ Q.take 10 $ Q.drop targetLength recipes
  20     where (State _ _ recipes) = last $ takeWhile unfinished1 $ states state0
  21
  22 unfinished1 :: State -> Bool
  23 unfinished1 (State _ _ recipes) = (Q.length recipes) <= (targetLength + 10)
  24
  25 part2 :: State -> Int
  26 part2 state0 = if (takeR (Q.length targetSeq) recipes) == targetSeq
  27                then (Q.length recipes) - (Q.length targetSeq)
  28                else (Q.length recipes) - (Q.length targetSeq) - 1
  29     where (State _ _ recipes) = head $ dropWhile (unfinished2 targetSeq) $ states state0
  30
  31 unfinished2 :: Recipes -> State -> Bool
  32 unfinished2 target (State _ _ recipes) =
  33     ((takeR (Q.length target) recipes) /= target)
  34     &&
  35     ((Q.take (Q.length target) (takeR (1 + Q.length target) recipes)) /= target)
  36
  37 states :: State -> [State]
  38 states = iterate extend
  39
  40 extend :: State -> State
  41 extend (State e1 e2 recipes) = State e1' e2' recipes'
  42     where v1 = Q.index recipes e1
  43           v2 = Q.index recipes e2
  44           total = v1 + v2
  45           recipes' = if total >= 10
  46                      then recipes |> (total `div` 10) |> (total `mod` 10)
  47                      else recipes |> total
  48           e1' = (e1 + v1 + 1) `mod` (Q.length recipes')
  49           e2' = (e2 + v2 + 1) `mod` (Q.length recipes')
  50
  51 targetSeq :: Recipes
  52 targetSeq = Q.fromList $ map read $ map (take 1 . drop 1) $ map show $ show targetLength
  53
  54 takeR n s = Q.drop (Q.length s - n) s