day5: add haskell solution

common/AoC.hs

@@ -1,9 +1,16 @@
 module AoC where
 
+import Text.ParserCombinators.ReadP
+
 (.:) :: (c -> d) -> (a -> b -> c) -> a -> b -> d
 f .: g = (f .) . g
 infixl 8 .:
 
+oneCompleteResult :: ReadP a -> String -> Maybe a
+oneCompleteResult p s = case readP_to_S (p <* eof) s of
+                          [(x, "")] -> Just x
+                          _ -> Nothing
+
 runAoC :: (Show r1, Show r2) => (String -> i) -> (i -> r1) -> (i -> r2) -> IO ()
 runAoC inputTransform part1 part2 = do
     contents <- inputTransform <$> getContents

day4/day4.hs

@@ -89,11 +89,6 @@ parseFieldNames = spaceSeparated parseFieldName
 parsePassport :: ReadP [Field]
 parsePassport = spaceSeparated parseField
 
-oneCompleteResult :: ReadP a -> String -> Maybe a
-oneCompleteResult p s = case readP_to_S (p <* eof) s of
-                          [(x, "")] -> Just x
-                          _ -> Nothing
-
 splitOnEmptyLines :: String -> [String]
 splitOnEmptyLines = map (intercalate " ") . filter (not . any null) . groupBy ((==) `on` null) . lines
 

day5/day5.hs

@@ -0,0 +1,23 @@
+import AoC
+
+import Data.List (sort)
+import Data.Maybe (fromJust)
+import Numeric (readInt)
+import Text.ParserCombinators.ReadP
+
+binarify :: String -> Maybe Int
+binarify = oneCompleteResult . readS_to_P $ readInt 2 (`elem` "BFLR") digitValue
+    where digitValue 'F' = 0
+          digitValue 'B' = 1
+          digitValue 'L' = 0
+          digitValue 'R' = 1
+
+findHole :: (Enum a, Eq a) => [a] -> Maybe a
+findHole (x:y:ys) | y == next = findHole $ y:ys
+                  | otherwise = Just next
+                  where next = succ x
+findHole _ = Nothing
+
+main = runAoC (fmap (fromJust . binarify) <$> lines) part1 part2
+    where part1 = foldr1 max
+          part2 = fromJust . findHole . sort