feat: day 2 part 2

src/Day2.hs

@@ -11,21 +11,30 @@ type Level = Int
 type Report = [Level]
 
 partOne :: String -> Either Error Int
-partOne contents = length . filter isValidReport <$> parseInput contents
-  where
-    isValidReport xs = isValidReportWith isSafeIncrease xs || isValidReportWith isSafeDecrease xs
-
-    isSafeIncrease x y = (x - y) > 0 && (x - y) < 4
-    isSafeDecrease x y = isSafeIncrease y x
-
-    isValidReportWith validator (x : y : xs) = validator x y && isValidReportWith validator (y : xs)
-    isValidReportWith _ [_] = True
-    isValidReportWith _ [] = False
+partOne contents = length . filter isSafeReport <$> parseInput contents
 
 partTwo :: String -> Either Error Int
-partTwo contents = calculateScore <$> parseInput contents
+partTwo contents = length . filter isSafeReportWithTolerance <$> parseInput contents
   where
-    calculateScore _ = 0
+    isSafeReportWithTolerance :: Report -> Bool
+    isSafeReportWithTolerance xs = isSafeReport xs || aux [] xs
+      where
+        aux left [] = isSafeReport left
+        aux left (x : xs') = isSafeReport (left ++ xs') || aux (left ++ [x]) xs'
+
+isSafeReport :: Report -> Bool
+isSafeReport xs = isSafeReportWith isSafeIncrease xs || isSafeReportWith isSafeDecrease xs
+
+isSafeReportWith :: (Level -> Level -> Bool) -> Report -> Bool
+isSafeReportWith validator (x : y : xs) = validator x y && isSafeReportWith validator (y : xs)
+isSafeReportWith _ [_] = True
+isSafeReportWith _ [] = False
+
+isSafeIncrease :: Level -> Level -> Bool
+isSafeIncrease x y = (x - y) > 0 && (x - y) < 4
+
+isSafeDecrease :: Level -> Level -> Bool
+isSafeDecrease x y = isSafeIncrease y x
 
 parseInput :: String -> Either Error [Report]
 parseInput contents = mapM parseReport (lines contents)