2024 day 2: Haskell solution

2024/2/Main1.hs

@@ -0,0 +1,14 @@
+import           Data.List.Split (splitOn)
+
+lineSafe :: [Int] -> Bool
+lineSafe [] = True
+lineSafe l@(_:xs) = (all (> 0) diffs || all (< 0) diffs) && all validItem diffs
+  where
+    diffs = zipWith (-) xs l
+
+    validItem x = x /= 0 && abs x <= 3
+
+main :: IO ()
+main = print . length . filter testLine . lines =<< readFile "data.txt"
+  where
+    testLine = lineSafe . map read . splitOn " "

2024/2/Main2.hs

@@ -0,0 +1,22 @@
+import           Data.List.Split (splitOn)
+
+lineSafe' :: [Int] -> Bool
+lineSafe' [] = True
+lineSafe'
+  l@(_:xs) = (all (> 0) diffs || all (< 0) diffs) && all validItem diffs
+  where
+    diffs = zipWith (-) xs l
+
+    validItem x = x /= 0 && abs x <= 3
+
+allRemoved :: [a] -> [[a]]
+allRemoved [] = []
+allRemoved (x:xs) = xs:map (x:) (allRemoved xs)
+
+lineSafe :: [Int] -> Bool
+lineSafe = any lineSafe' . allRemoved
+
+main :: IO ()
+main = print . length . filter testLine . lines =<< readFile "data.txt"
+  where
+    testLine = lineSafe . map read . splitOn " "

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1712963716,
+        "lastModified": 1733015953,
-        "narHash": "sha256-WKm9CvgCldeIVvRz87iOMi8CFVB1apJlkUT4GGvA0iM=",
+        "narHash": "sha256-t4BBVpwG9B4hLgc6GUBuj3cjU7lP/PJfpTHuSqE+crk=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "cfd6b5fc90b15709b780a5a1619695a88505a176",
+        "rev": "ac35b104800bff9028425fec3b6e8a41de2bbfff",
         "type": "github"
       },
       "original": {

flake.nix

@@ -27,6 +27,8 @@
                 split-sequence
                 str
               ]))
+            pkgs.haskell-language-server
+            pkgs.stylish-haskell
             (pkgs.ghc.withPackages (p:
               with p; [
                 containers