cleanup

solutions/solutions.cabal

@@ -1151,4 +1151,4 @@ executable sln_2024_07
 executable sln_2024_08
   import:              day
   main-is:             2024/08.hs
-  build-depends:       containers
+  build-depends:       array, containers

solutions/src/2024/08.hs

@@ -8,42 +8,65 @@ Maintainer  : emertens@gmail.com
 
 <https://adventofcode.com/2024/day/8>
 
+>>> :{
+:main + "............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............
+"
+:}
+14
+34
+
 -}
 module Main (main) where
 
-import Advent (getInputMap)
-import Advent.Coord (coordRow, coordCol, Coord (C))
-import Control.Monad (guard)
-import Data.List (nub, tails)
+import Advent (getInputArray)
+import Advent.Coord (Coord(C))
+import Data.Array.Unboxed (assocs, bounds, inRange)
+import Data.List (tails)
 import Data.Map qualified as Map
+import Data.Set qualified as Set
 
 -- | >>> :main
 -- 303
 -- 1045
 main :: IO ()
 main =
- do input <- getInputMap 2024 8
-    let locs = Map.filter (\x -> length x > 1)
-             $ Map.fromListWith (++) [(v, [k]) | (k,v) <- Map.assocs input, v /= '.']
-    print $ length $ nub $
-     do posns <- Map.elems locs
-        x:ys <- tails posns
-        y <- ys
-        node <- [y + (y - x), x + (x - y)]
-        guard (Map.member node input)
-        pure node
-    print $ length $ nub $ concat (Map.elems locs) ++
-     do posns <- Map.elems locs
-        x:ys <- tails posns
-        y <- ys
-        z <- Map.keys input
-        guard (inlined x y z)
-        [z,x,y]
-
-inlined :: Coord -> Coord -> Coord -> Bool
-inlined x y z
-  | coordCol x == coordCol z = coordCol x == coordCol y
-  | otherwise = coordCol z /= coordCol y && slope z x == slope y x
+ do input <- getInputArray 2024 8
+    let antennaGroups = Map.elems (Map.fromListWith (++) [(v, [k]) | (k, v) <- assocs input, v /= '.'])
+    print (length (Set.fromList
+      [ node
+      | antennaGroup <- antennaGroups
+      , x:ys <- tails antennaGroup
+      , y    <- ys
+      , node <- [2 * y - x, 2 * x - y]
+      , inRange (bounds input) node
+      ]))
+    print (length (Set.fromList
+      [ node
+      | antennaGroup <- antennaGroups
+      , x:ys <- tails antennaGroup
+      , y    <- ys
+      , node <- nodeLine (inRange (bounds input)) x y
+      ]))
 
-slope :: Coord -> Coord -> Rational
-slope (C y1 x1) (C y2 x2) = fromIntegral (y2-y1) / fromIntegral (x2-x1)
+-- | Generate all the points on the line defined by two coordinates
+-- that fit inside a bounding box predicate.
+nodeLine :: (Coord -> Bool) -> Coord -> Coord -> [Coord]
+nodeLine p a b =
+   takeWhile p (iterate (step +) a) ++
+   takeWhile p (iterate (subtract step) (a - step))
+  where
+    C dy dx                  = a - b
+    com | dx == 0 || dy == 0 = 1
+        | otherwise          = gcd dy dx
+    step                     = C (dy `quot` com) (dx `quot` com)