Day 2 gold star

02/gold.hs

@@ -0,0 +1,21 @@
+isSortedGradually' :: (Integer -> Integer -> Bool) -> Bool -> [Integer] -> Bool
+isSortedGradually' f mercy (x1:x2:xs) =
+    (diff >= 1 && diff <= 3 && f x1 x2 && isSortedGradually' f mercy (x2:xs))
+        || mercy && isSortedGradually' f False (x1:xs)
+       where diff = abs (x1 - x2)
+isSortedGradually' f mercy _ = True
+
+isSortedGradually f (x:xs) = isSortedGradually' f True (x:xs)
+                          || isSortedGradually' f False xs
+
+isAscending  :: [Integer] -> Bool
+isAscending xs  = isSortedGradually (<) xs
+
+isDescending :: [Integer] -> Bool
+isDescending xs = isSortedGradually (>) xs
+
+isSafe :: [Integer] -> Bool
+isSafe xs = isAscending xs || isDescending xs
+
+main :: IO() 
+main = interact $ show . sum . map (fromEnum . isSafe . map read . words) . lines