do not use intermediate sets

2021/day20.hs

@@ -6,14 +6,14 @@ import Debug.Trace (traceShow, trace)
 import Data.Maybe (catMaybes)
 
 type Algorithm = A.Array Int Bool
-data Image = Img Bool (S.Set (Int,Int)) deriving (Show)
+data Image = Img Bool [(Int,Int)] deriving (Show)
 
-getNd :: Image -> S.Set (Int,Int)
+getNd :: Image -> [(Int,Int)]
 getNd (Img _ s) = s
 
 getLit :: Image -> Int
 getLit (Img True s) = error "all elems lit"
-getLit (Img False s) = length $ S.elems s
+getLit (Img False s) = length s
 
 newDefault :: Algorithm -> Bool -> Bool
 newDefault algo False = algo A.! 0
@@ -32,17 +32,17 @@ next algo (Img def diff) = Img (newDefault algo def) newDiff where
     neighs x y = map (\i -> ((x-1 + i `mod` 3, y-1 + i `div` 3), [i])) [0..8]
     calcNonDef = M.filter (/= newDefault algo def) $ M.map (\ns -> algo A.! binToDec (nonDefToNum ns)) nonDefault
     nonDefToNum ns = map (\i -> if i `elem` ns then not def else def) [0..8]
-    newDiff = S.fromList $ M.keys calcNonDef
+    newDiff = M.keys calcNonDef
 
 printImage :: Image -> IO ()
 printImage img = do
     mapM_ (\y -> do
-        mapM_ (\x -> if (x,y) `S.member` getNd img then putChar '#' else putChar '.') [minx..maxx];
+        mapM_ (\x -> if (x,y) `elem` getNd img then putChar '#' else putChar '.') [minx..maxx];
         putStrLn "") [miny..maxy] where
-    minx = minimum $ map fst $ S.elems $ getNd img
-    maxx = maximum $ map fst $ S.elems $ getNd img
-    miny = minimum $ map snd $ S.elems $ getNd img
-    maxy = maximum $ map snd $ S.elems $ getNd img
+    minx = minimum $ map fst $ getNd img
+    maxx = maximum $ map fst $ getNd img
+    miny = minimum $ map snd $ getNd img
+    maxy = maximum $ map snd $ getNd img
 
 
 main :: IO()
@@ -51,29 +51,16 @@ main = do
     getLine
     content <- lines <$> getContents
     let nonDef = catMaybes $ concat $ zipWith (\j -> zipWith (\i e -> if e =='#' then Just (i,j) else Nothing) [0..]) [0..] content
-    let init = Img False $ S.fromList nonDef
+    let init = Img False nonDef
 
-    mapM_ print content
-    putStr "initial: "
-    print init
-    printImage init
-
-    putStr "after 1: "
-    let first = next algorithm init
-    print first
-    printImage first
-
-    putStr "after 2: "
-    let second = next algorithm first
-    print second
-    printImage second
 
+    let enhanced = iterate (next algorithm) init
     putStr "part 1: "
-    print $ getLit second
+    print $ getLit $ enhanced !! 2
 
-    let enhanced = iterate (next algorithm) init !! 50
+    -- let enhanced = iterate (next algorithm) init !! 50
     putStr "part 2: "
-    print $ getLit enhanced
+    print $ getLit $ enhanced !! 50