[hs] Solve 2020_02

hs/src/Aoc/Y2020/D02.hs

@@ -0,0 +1,44 @@
+module Aoc.Y2020.D02
+  ( day
+  ) where
+
+import qualified Data.Text     as T
+
+import           Aoc.Day
+import           Aoc.Parse
+
+data Line = Line
+  { lMin  :: Int
+  , lMax  :: Int
+  , lChar :: Char
+  , lPw   :: T.Text
+  }
+
+parser :: Parser [Line]
+parser = manyLines $ Line
+  <$> (decimal <* char '-')
+  <*> (decimal <* space)
+  <*> (anySingle <* char ':' <* space)
+  <*> untilEol
+
+validCount :: Line -> Bool
+validCount l = n >= lMin l && n <= lMax l
+  where
+    n = T.count (T.singleton $  lChar l) $ lPw l
+
+validPositions :: Line -> Bool
+validPositions l = (left == lChar l) /= (right == lChar l)
+  where
+    left = T.index (lPw l) (lMin l - 1)
+    right = T.index (lPw l) (lMax l - 1)
+
+solver :: [Line] -> IO ()
+solver ls = do
+  putStrLn ">> Part 1"
+  print $ length $ filter validCount ls
+
+  putStrLn ">> Part 2"
+  print $ length $ filter validPositions ls
+
+day :: Day
+day = dayParse "2020_02" parser solver