day8.hs

module Day8 where

import Data.Map.Strict qualified as Map
import Data.List
import Data.Containers.ListUtils (nubOrd)

main :: IO ()
main = do
  input <- readFile "day8.txt"
  let (width, height) = (length (head (lines input)), length (lines input))
  let antennas = groupBy (\(_, a) (_, b) -> a == b) $ sortBy (\(_, a) (_, b) -> compare a b) $ filter ((/= '.') . snd) [((j :: Int, i :: Int), c) | (line, i) <- zip (lines input) [0..], (c, j) <- zip line [0..]]
  let maxN = max width height
  let isValid (x, y) = x >= 0 && x < width && y >= 0 && y < height
  let getAntinodes (x1, y1) (x2, y2) = filter isValid [(x2 - n * (x1 - x2), y2 - n * (y1 - y2)) | n <- [-maxN..maxN]]
  let antinodes = nubOrd $ concat $ fmap (\xs -> concat [(getAntinodes a b) | a <- xs, b <- xs, a /= b]) $ fmap (fmap fst) antennas
  print $ length antinodes