Day 2 parts 1 and 2

day2/main.hs

@@ -1,10 +1,85 @@
 #! /usr/bin/env -S"ANSWER=42" nix-shell
 #! nix-shell -p ghcid
-#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [shower])"
+#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [attoparsec])"
 #! nix-shell -i "ghcid -c 'ghci -Wall' -T main"
 
 {-# LANGUAGE OverloadedStrings #-}
 
+import Data.Attoparsec.Text
+import Data.Text (pack)
+import Data.Maybe (catMaybes)
+import Data.Bits (xor)
+
+testData :: [String]
+testData = [ "1-3 a: abcde"
+           , "1-3 b: cdefg"
+           , "2-9 c: ccccccccc"
+           ]
+
+data Input = Input {
+  atLeast :: Int
+, notMore :: Int
+, character :: Char
+, password :: String
+} deriving Show
+
+inputParser :: Parser Input
+inputParser = do
+  atLeast'    <- decimal
+  _           <- char '-'
+  notMore'    <- decimal
+  _           <- space
+  character'  <- letter
+  _           <- char ':'
+  _           <- space
+  password'   <- many1 letter
+  return $ Input atLeast' notMore' character' password'
+
+parseInputLine :: String -> Maybe Input
+parseInputLine s = eitherToMaybe $ parseOnly inputParser (pack s)
+
+eitherToMaybe :: Either a b -> Maybe b
+eitherToMaybe (Right e) = Just e
+eitherToMaybe (Left _) = Nothing
+
+match' :: Char -> Char -> Int
+match' c1 c2 | c1 == c2 = 1
+match' _ _ = 0
+
+-- How many passwords are valid according to their policies?
+
+validatePassword1 :: Input -> Bool
+validatePassword1 (Input min' max' char' pass) =
+  c >= min' && c <= max'
+  where
+    c = foldl (\acc c' -> acc + match' char' c') 0 pass
+
+-- How many passwords are valid according to the new interpretation of the
+-- policies?
+
+validatePassword2 :: Input -> Bool
+validatePassword2 (Input pos1 pos2 char' pass) =
+  (pass !! (pos1-1) == char') `xor` (pass !! (pos2-1) == char')
+
+validateLine :: (Input -> Bool) -> String -> Maybe Bool
+validateLine f s = do
+  i <- parseInputLine s
+  pure $ f i
+
+countTrue :: [Bool] -> Int
+countTrue = length . filter (== True)
+
+solveDay2Part1 :: [String] -> Int
+solveDay2Part1 = countTrue . catMaybes . (map (validateLine validatePassword1))
+
+solveDay2Part2 :: [String] -> Int
+solveDay2Part2 = countTrue . catMaybes . (map (validateLine validatePassword2))
+
 main :: IO ()
 main = do
   putStrLn "Day 2 - Part 1"
+  inputData <- readFile "./day2/input"
+  print $ solveDay2Part1 testData
+  print $ solveDay2Part1 (lines inputData)
+  print $ solveDay2Part2 testData
+  print $ solveDay2Part2 (lines inputData)