Day 2

Day2/puzzle1.hs

@@ -0,0 +1,14 @@
+import Data.List (sort)
+import System.IO
+
+isSafe :: [Int] -> Bool
+isSafe xs = (isAscending xs || isDescending xs) && maximum distances <= 3 && minimum distances >= 1
+            where isAscending xs = xs == sort xs
+                  isDescending xs = xs == reverse (sort xs)
+                  distances = map abs $ zipWith (-) xs (tail xs)
+
+main = do
+    contents <- lines <$> readFile "day2.txt"
+    let reports = map read . words <$> contents
+        safeCount = length $ filter isSafe reports
+    print safeCount

Day2/puzzle2.hs

@@ -0,0 +1,19 @@
+import Data.List (sort, inits, tails)
+import System.IO
+
+isSafe :: [Int] -> Bool
+isSafe xs = (isAscending xs || isDescending xs) && maximum distances <= 3 && minimum distances >= 1
+            where isAscending xs = xs == sort xs
+                  isDescending xs = xs == reverse (sort xs)
+                  distances = map abs $ zipWith (-) xs (tail xs)
+
+removeLevel :: [Int] -> [[Int]]
+removeLevel xs = zipWith (++) ys zs
+            where ys = map init $ tail (inits xs)
+                  zs = map tail $ init (tails xs)
+
+main = do
+    contents <- lines <$> readFile "day2.txt"
+    let reports = map read . words <$> contents
+        safeCount = length . filter (any isSafe) $ map removeLevel reports
+    print safeCount