Haskell variant for day seven

day-07-haskell/src/Common.hs

@@ -0,0 +1,3 @@
+module Common (Equation) where
+
+type Equation = (Int, [Int])

day-07-haskell/src/Lib.hs

@@ -0,0 +1,6 @@
+module Lib
+    ( someFunc
+    ) where
+
+someFunc :: IO ()
+someFunc = putStrLn "someFunc"

day-07-haskell/src/Task1.hs

@@ -0,0 +1,20 @@
+module Task1 (task1) where
+
+import Common
+
+task1 :: [Equation] -> Int
+task1 equations = sum $ map processEquation equations
+
+processEquation :: Equation -> Int
+processEquation (result, params) =
+  if brute (reverse params) result
+  then result
+  else 0
+  where
+    brute :: [Int] -> Int -> Bool
+    brute [] _ = False
+    brute [param] subResult = subResult == param
+    brute (param:subParams) subResult
+      | brute subParams $ subResult - param = True
+      | subResult `mod` param == 0 && brute subParams (subResult `div` param) = True
+      | otherwise = False

day-07-haskell/src/Task2.hs

@@ -0,0 +1,34 @@
+module Task2 (task2, unconcat, unconcatStrings) where
+
+import Common
+import Data.List (isSuffixOf)
+
+task2 :: [Equation] -> Int
+task2 equations = sum $ map processEquation equations
+
+processEquation :: Equation -> Int
+processEquation (result, params) =
+  if brute (reverse params) result
+  then result
+  else 0
+  where
+    brute :: [Int] -> Int -> Bool
+    brute [] _ = False
+    brute [param] subResult = subResult == param
+    brute (param:subParams) subResult
+      | brute subParams $ subResult - param = True
+      | subResult `mod` param == 0 && brute subParams (subResult `div` param) = True
+      | otherwise = case unconcat subResult param of
+        Nothing -> False
+        Just rest -> brute subParams rest
+
+unconcat :: Int -> Int -> Maybe Int
+unconcat result suffix = do
+  rest <- unconcatStrings (show result) (show suffix)
+  Just $ read rest
+
+unconcatStrings :: String -> String -> Maybe String
+unconcatStrings sResult sSuffix
+  | sSuffix == sResult = Nothing
+  | sSuffix `isSuffixOf` sResult = Just $ take ((length sResult) - (length sSuffix)) sResult
+  | otherwise = Nothing