day9 part 2

2022/day09/day09.hs

@@ -1,13 +1,22 @@
 import Linear.V2
 import Data.List
+import Data.List.Split
 import Control.Lens
 
 type Rope = (V2 Int,V2 Int)
 
 main :: IO ()
 main = do
-  input <- concat <$> map (parse . words) <$> lines <$> readFile "input"
-  print $ length $ nub $ sort $ snd $ moveAll ((V2 0 0,V2 0 0),[]) input
+  input <- concat <$> map (parse . words) <$> lines <$> readFile "input" --should be 4, is 1
+  print $ length $ nub $ day9 1 input
+  print $ length $ nub $ day9 9 input
+--  putStrLn $ intercalate "\n" $ print2D 10 $ sort $ nub $ day9 3 input
+
+day9 :: Int -> [V2 Int] -> [V2 Int]
+day9 n input
+  | n > 1 = day9 (pred n) (zipWith (-) (tail field) field)
+  | otherwise = field
+  where field = concat $ map nub $ group $ reverse $ snd $ moveAll ((V2 0 0,V2 0 0),[]) input
 
 parse :: [String] -> [V2 Int]
 parse (dir:len:[])
@@ -27,6 +36,18 @@ move ((head,tail),ps) m = ((head+m,newTail),tail:ps)
 
 tailMove (V2 a b) = V2 (f a) (f b)
     where f x
-            | abs a == abs b = 0
+            | abs a == abs b = if abs a == 2 then x `div` 2 else 0
             | abs a + abs b == 1 = 0
-            | otherwise = if abs x >= 2 then x `div` 2 else x
+            | otherwise = if abs x == 2 then x `div` 2 else x
+
+p :: Int -> [Int] -> String
+p n (x:xs) = if n == x then '#' : p (n+1) xs else '.' : p (n+1) (x:xs)
+p _ [] = []
+
+print2D :: Int -> [V2 Int] -> [String]
+print2D n coords
+  | n == (pred minY) = []
+  | otherwise = p minX line : print2D (n-1) coords
+  where line = sort $ map (^._x) (filter (\(V2 _ a) -> a == n) coords)
+        minY = minimum $ map (^._y) coords
+        minX = minimum $ map (^._x) coords