haskell: 2015 04

2015/haskell/haskell.cabal

@@ -20,12 +20,22 @@ library
     Day01
     Day02
     Day03
+    Day04
+
+  default-extensions:
+    ImportQualifiedPost
+    OverloadedStrings
 
   -- Modules included in this library but not exported.
   -- other-modules:
   -- LANGUAGE extensions used by modules in this package.
   -- other-extensions:
-  build-depends: base >=4.16.4.0
+  build-depends:
+    base >=4.16.4.0,
+    bytestring >=0.10.10.0,
+    cryptohash-md5 >=0.11.101.0,
+    text >=2.1.1,
+
   hs-source-dirs: solutions
   default-language: Haskell2010
 
@@ -36,9 +46,8 @@ executable haskell
   -- LANGUAGE extensions used by modules in this package.
   -- other-extensions:
   build-depends:
-    base     >= 4.16.4.0,
-    text     >= 2.1.1,
     aoc2015,
+    base >=4.16.4.0,
 
   hs-source-dirs: app
   default-language: Haskell2010

2015/haskell/solutions/Day04.hs

@@ -0,0 +1,26 @@
+module Day04 (solveA, solveB) where
+
+import Crypto.Hash.MD5 (hash)
+import Data.Bifunctor (second)
+import Data.ByteString (ByteString)
+import Data.ByteString qualified as BS
+import Data.ByteString.Char8 qualified as Char8
+import Text.Printf (printf)
+
+hashHex :: String -> String
+hashHex = concatMap (printf "%02x") . BS.unpack . hash . Char8.pack
+
+test :: String
+test = "ckczppom"
+
+solve :: Int -> String -> Integer
+solve zeros key = fst . head . filter (isMatch . snd) . map toHash $ [1 ..]
+ where
+  toHash n = (n, hashHex $ key <> show n)
+  isMatch = all (== '0') . take zeros
+
+solveA :: String -> Integer
+solveA = solve 5
+
+solveB :: String -> Integer
+solveB = solve 6