Done day 8

diff --git a/advent08/Main.hs b/advent08/Main.hs
new file mode 100644 (file)
index 0000000..d7684a4
--- /dev/null
+++ b/advent08/Main.hs
@@ -0,0 +1,53 @@
+-- Writeup at https://work.njae.me.uk/2024/12/08/advent-of-code-2024-day-8/
+
+import AoC
+import Linear
+import Data.List
+import Data.Ix
+import qualified Data.Map.Strict as M
+
+type Position = V2 Int -- r, c
+type Bounds = (Position, Position)
+type Grid = M.Map Char [Position]
+
+main :: IO ()
+main = 
+  do  dataFileName <- getDataFileName
+      text <- readFile dataFileName
+      let (bounds, antennas) = mkGrid text
+      -- print antennas
+      -- print bounds
+      -- print $ allFreqAntinodes bounds antennas
+      -- print $ length $ nub $ concat $ M.elems $ allFreqAntinodes bounds antennas
+      print $ part1 bounds antennas
+      print $ part2 bounds antennas
+
+part1, part2 :: Bounds -> Grid -> Int
+part1 bounds antennas = length $ nub $ concat $ M.elems $ allFreqAntinodes bounds antennas
+part2 bounds antennas = length $ nub $ concat $ M.elems $ allFreqHarmonicAntinodes bounds antennas
+
+allFreqAntinodes, allFreqHarmonicAntinodes :: Bounds -> Grid -> Grid
+allFreqAntinodes bounds = M.map (antinodesOf bounds)
+allFreqHarmonicAntinodes bounds = M.map (harmonicAntinodesOf bounds)
+
+antinodesOf, harmonicAntinodesOf :: Bounds -> [Position] -> [Position]
+antinodesOf bounds ps = 
+  filter (inRange bounds) [2 *^ a ^-^ b | a <- ps, b <- ps, a /= b]
+
+harmonicAntinodesOf bounds@(_, V2 kMax _) ps = 
+  filter (inRange bounds) [ a ^+^ k *^ (a ^-^ b)
+                          | a <- ps, b <- ps, a /= b
+                          , k <- [0 .. kMax]]
+
+mkGrid :: String -> (Bounds, Grid)
+mkGrid text = ((V2 0 0, V2 rMax cMax), 
+              foldl' go M.empty points)
+  where rows = lines text
+        rMax = length rows - 1
+        cMax = (length $ head rows) - 1
+        points =  [ (rows !! r !! c, V2 r c) 
+                  | r <- [0..rMax], c <- [0..cMax]
+                  , rows !! r !! c /= '.'
+                  ]
+        go grid (f, pos) = M.insertWith (++) f [pos] grid
+

diff --git a/adventofcode24.cabal b/adventofcode24.cabal
index 87c1a445a6966ed193ab25b5d4b8699f53d04f6f..74d0048092bb38ac246f3256777f51bd69542d46 100644 (file)
--- a/adventofcode24.cabal
+++ b/adventofcode24.cabal
@@ -113,4 +113,9 @@ executable advent07
   import: warnings, common-extensions, build-directives, common-modules
   main-is: advent07/Main.hs  
   build-depends: attoparsec, text
+
+executable advent08
+  import: warnings, common-extensions, build-directives, common-modules
+  main-is: advent08/Main.hs  
+  build-depends: linear, containers
   
\ No newline at end of file