day3 part1

2021/day03/day03.hs

@@ -0,0 +1,13 @@
+import Data.List
+import Control.Lens
+import Control.Arrow
+
+main :: IO ()
+main = do
+  input <- lines <$> readFile "input"
+  let counts = map ((\[x,y]->x>y) . map length . group . sort) $ transpose input
+  let (gamma,epsilon) = boolToDec *** boolToDec $ (id &&& map not) counts
+  print $ gamma * epsilon
+
+boolToDec :: [Bool] -> Int
+boolToDec = sum . imap (\x y->(2^x)*y) . reverse . map fromEnum