Day 2 silver star

02/silver.hs

@@ -0,0 +1,20 @@
+
+import Debug.Trace
+
+debug = flip trace
+
+isSortedGradually :: (Integer -> Integer -> Bool) -> [Integer] -> Bool
+isSortedGradually f (x1:x2:xs) = (f x1 x2) && diff >= 1 && diff <= 3 && isSortedGradually f (x2:xs)
+    where diff = abs (x1 - x2)
+isSortedGradually f (x1:_) = True
+isSortedGradually f _ = True
+
+isAscending  :: [Integer] -> Bool
+isAscending = isSortedGradually (<)
+isDescending :: [Integer] -> Bool
+isDescending = isSortedGradually (>)
+
+ok xs = isAscending xs || isDescending xs
+
+main :: IO() 
+main = interact $ show . sum . map (fromEnum . ok . map (read :: (String -> Integer)) . words) . lines

02/test.txt

@@ -0,0 +1,6 @@
+7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9