initialise repo; add days 1-3

03/solution.hs

@@ -0,0 +1,57 @@
+import Debug.Trace
+import Data.Maybe
+import Control.Applicative
+
+instance (Applicative m, Num a) => Num (m a) where
+  (+) = liftA2 (+)
+  (-) = liftA2 (-)
+  (*) = liftA2 (*)
+  abs = fmap abs
+  signum = fmap signum
+  negate = fmap negate
+  fromInteger = pure . fromInteger
+
+traceOut :: Show a => a -> a
+traceOut x = traceShow x x
+
+addFirst :: [[a]] -> a -> [[a]]
+addFirst [] x = [[x]]
+addFirst (y:ys) x = ([x] ++ y) : ys
+
+split :: Eq a => [a] -> [a] -> [[a]]
+split _ [] = []
+split delims (x:xs)
+  | elem x delims = [[]] ++ split delims xs
+  | otherwise     = addFirst (split delims xs) x
+
+parseFile :: String -> [[Int]]
+parseFile = map (map (read . (:[]))) . split ['\n']
+
+dropLast :: Int -> [a] -> [a]
+dropLast n = reverse . drop n . reverse
+
+takeAfter :: (a -> Bool) -> [a] -> [a]
+takeAfter f [] = []
+takeAfter f (x:xs) = if f x then xs else takeAfter f xs
+
+listMax :: Ord a => [a] -> Maybe a
+listMax [] = Nothing
+listMax (x:xs) = Just $ foldl max x xs
+
+bestJoltage :: Int -> [Int] -> Maybe Int
+bestJoltage n xs
+  | n <= 0               = 0
+  | null (drop (n-1) xs) = 0
+  | otherwise            = case maximum of Nothing -> Nothing; Just maximum' -> 10^(n-1) * maximum + (bestJoltage (n-1) (takeAfter (>= maximum') xs))
+        where maximum = listMax $ dropLast (n-1) xs
+
+solve :: Int -> [[Int]] -> Maybe Int
+solve n = fmap sum . sequence . map (bestJoltage n)
+
+main = do 
+    fileinp <- readFile "input.txt"
+    let input = parseFile fileinp
+    let solved1 = fromJust $ solve 2 input
+    let solved2 = fromJust $ solve 12 input
+    print solved1
+    print solved2