Solution for 4

4/4.hs

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+{-# LANGUAGE Strict #-}
+module Main where
+
+import Control.Applicative (some)
+import Data.Function (on)
+import Data.List (sort, foldl', maximumBy, groupBy, sortOn)
+import Data.List.Split (split, dropInitBlank, keepDelimsL, whenElt, chunksOf)
+import qualified Data.Map as M
+import Data.Time (LocalTime, diffUTCTime, localTimeToUTC, utc, todMin, localTimeOfDay)
+import Data.Time.Clock (NominalDiffTime)
+import Data.Time.Format (parseTimeOrError, defaultTimeLocale)
+import Text.Parsec
+
+type GuardId = Int
+data Action = BeginShift GuardId
+            | FallAsleep
+            | WakeUp
+            deriving (Show, Eq)
+data Record = Record { recTime :: LocalTime, recAction :: Action }
+              deriving (Show, Eq)
+type Round = [Record]
+
+shiftBeginning :: Record -> Bool
+shiftBeginning (Record _ (BeginShift _)) = True
+shiftBeginning _                         = False
+
+instance Ord Record where
+  compare = compare `on` recTime
+
+parseTime :: String -> LocalTime
+parseTime = parseTimeOrError False defaultTimeLocale "%F %R"
+
+diffLocalTime :: LocalTime -> LocalTime -> NominalDiffTime
+diffLocalTime a b = diffUTCTime (localTimeToUTC utc a) (localTimeToUTC utc b)
+
+inputP :: Parsec String () Record
+inputP = Record <$> (tsP <* space) <*> (bsP <|> wP <|> aP)
+  where
+    intP = read <$> some digit
+    tsP = parseTime <$> (char '[' *> some (noneOf "]") <* char ']')
+
+    bsP =  BeginShift
+          <$> (string "Guard" *> space *> char '#' *> intP <* space <* string "begins shift")
+
+    wP = WakeUp <$ string "wakes up"
+    aP = FallAsleep <$ string "falls asleep"
+
+readInput :: [String] -> [Record]
+readInput ls = case traverse (parse inputP "") ls of
+  Left e -> error (show e)
+  Right rs -> sort rs
+
+splitRounds :: [Record] -> [[Record]]
+splitRounds = split $ dropInitBlank $ keepDelimsL $ whenElt shiftBeginning
+
+guardID :: Round -> GuardId
+guardID ~(Record _ (BeginShift gID) : _) = gID
+
+summarizeRounds :: [Round] -> (GuardId, Int, (Int, Int))
+summarizeRounds rounds =
+  (guardID $ head rounds,
+   totalSleep rounds,
+   case M.assocs minMap of
+     [] -> (-1, 0)
+     xs -> maximumBy (compare `on` snd) xs)
+  where
+    getMin = todMin . localTimeOfDay . recTime
+    
+    totalSleep = sum . map (sum . map (\[s,e] -> getMin e - getMin s) . chunksOf 2 . tail)
+    minMap = 
+      foldl' (\a r ->
+              foldl' (\a' [s,e] ->
+                      foldl' (\a'' m -> M.insertWith (+) m 1 a'') a' [getMin s .. (getMin e - 1)])
+                     a (chunksOf 2 . tail $ r))
+             M.empty rounds
+
+mostAsleep = maximumBy (compare `on` (\(_,t,_) -> t))
+mostAsleepOnSameMinute = maximumBy (compare `on` (\(_,_,(_,m)) -> m))
+
+main = do
+  rounds <- splitRounds . readInput . lines <$> getContents
+  let summary = map summarizeRounds . groupBy ((==) `on` guardID) . sortOn guardID $ rounds
+  putStrLn $ "Summary = " ++ show summary
+  putStrLn $ "Most asleep = " ++ show (mostAsleep summary)
+  putStrLn $ "Most asleep on same minute = " ++ show (mostAsleepOnSameMinute summary)

4/Setup.hs

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+import Distribution.Simple
+main = defaultMain

4/stack.yaml

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+resolver: lts-12.21
+
+packages:
+- .

4/x4.cabal

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+-- Initial x4.cabal generated by cabal init.  For further documentation,
+-- see http://haskell.org/cabal/users-guide/
+
+name:                x4
+version:             0.1.0.0
+-- synopsis:
+-- description:
+license:             BSD3
+author:              Abhinav Sarkar
+maintainer:          abhinav@abhinavsarkar.net
+-- copyright:
+-- category:
+build-type:          Simple
+cabal-version:       >=1.10
+
+executable x4
+  main-is:             4.hs
+  -- other-modules:
+  -- other-extensions:
+  build-depends:       base >=4.11 && <4.12
+                      ,split
+                      ,containers
+                      ,time
+                      ,parsec
+  ghc-options:        -O2
+  -- hs-source-dirs:
+  default-language:    Haskell2010