Day 05.

app/Main.hs

@@ -30,4 +30,4 @@ import qualified Day24
 import qualified Day25
 
 main :: IO ()
-main = Day04.main
+main = Day05.main

src/Day05.hs

@@ -1,6 +1,17 @@
 module Day05 (main) where
 
+import Data.Char (toLower)
+
+part1 :: String -> Int
+part1 = length . foldr react []
+    where react c [] = [c]
+          react c (u:us) = if (c /= u) && (toLower c == toLower u) then us else (c:u:us)
+
+part2 :: String -> Int
+part2 str = minimum . map (\c -> part1 . filter ((/= c) . toLower) $ str) $ ['a'..'z']
+
 main :: IO ()
 main = do
     input <- readFile "input/05.txt"
-    print input
+    print $ part1 input
+    print $ part2 input