day6: add haskell solution

README.md

@@ -11,3 +11,4 @@ https://adventofcode.com/2020/
 | 3 |  `**`  |  `**`   |      |
 | 4 |  `**`  |  `**`   |      |
 | 5 |        |  `**`   |      |
+| 6 |        |  `**`   |      |

common/AoC.hs

@@ -1,5 +1,7 @@
 module AoC where
 
+import Data.Function (on)
+import Data.List (groupBy, intercalate)
 import Text.ParserCombinators.ReadP
 
 (.:) :: (c -> d) -> (a -> b -> c) -> a -> b -> d
@@ -11,6 +13,9 @@ oneCompleteResult p s = case readP_to_S (p <* eof) s of
                           [(x, "")] -> Just x
                           _ -> Nothing
 
+splitOnEmptyLines :: String -> [[String]]
+splitOnEmptyLines = filter (not . any null) . groupBy ((==) `on` null) . lines
+
 runAoC :: (Show r1, Show r2) => (String -> i) -> (i -> r1) -> (i -> r2) -> IO ()
 runAoC inputTransform part1 part2 = do
     contents <- inputTransform <$> getContents

day3/day3.hs

@@ -23,6 +23,6 @@ countHits = length . filterMap lookup . catMaybes .: compose2 (zipWith mzip) may
 treeCharToBool :: Char -> Bool
 treeCharToBool = (== '#')
 
-main = runAoC (fmap (cycle . map treeCharToBool) <$> lines) part1 part2
+main = runAoC (map (cycle . map treeCharToBool) . lines) part1 part2
     where part1 = countHits (3, 1)
           part2 = product . (fmap countHits [(1,1), (3,1), (5,1), (7,1), (1,2)] ??)

day4/day4.hs

@@ -3,8 +3,6 @@ import AoC
 import Control.Applicative ((<|>))
 import Control.Monad (guard, mfilter)
 import Data.Char (isDigit)
-import Data.Function (on)
-import Data.List (groupBy, intercalate)
 import Data.Maybe (mapMaybe)
 import Text.ParserCombinators.ReadP
 import Text.Read (readMaybe)
@@ -89,13 +87,10 @@ parseFieldNames = spaceSeparated parseFieldName
 parsePassport :: ReadP [Field]
 parsePassport = spaceSeparated parseField
 
-splitOnEmptyLines :: String -> [String]
-splitOnEmptyLines = map (intercalate " ") . filter (not . any null) . groupBy ((==) `on` null) . lines
-
 hasAllRequiredFields :: String -> Bool
 hasAllRequiredFields = maybe False containsAllFields . fieldNames
     where requiredFieldNames = ["byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid"]
           containsAllFields fields = all (`elem` fields) requiredFieldNames
           fieldNames = oneCompleteResult parseFieldNames
 
-main = runAoC (filter hasAllRequiredFields . splitOnEmptyLines) (length) (length . mapMaybe (oneCompleteResult parsePassport))
+main = runAoC (filter hasAllRequiredFields . map (intercalate " ") . splitOnEmptyLines) (length) (length . mapMaybe (oneCompleteResult parsePassport))

day5/day5.hs

@@ -18,6 +18,6 @@ findHole (x:y:ys) | y == next = findHole $ y:ys
                   where next = succ x
 findHole _ = Nothing
 
-main = runAoC (fmap (fromJust . binarify) <$> lines) part1 part2
+main = runAoC (map (fromJust . binarify) . lines) part1 part2
     where part1 = foldr1 max
           part2 = fromJust . findHole . sort

day6/day6.hs

@@ -0,0 +1,9 @@
+import AoC
+
+import qualified Data.Set as S
+import           Data.Set (Set)
+
+main = runAoC ((fmap . fmap) S.fromList . splitOnEmptyLines) part1 part2
+    where part1 = countSetsFolded S.union
+          part2 = countSetsFolded S.intersection
+          countSetsFolded f = sum . map (S.size . foldr1 f)