day03.hs

-- Question: https://adventofcode.com/2015/day/3

import qualified Data.Set  as S
import           System.IO (readFile)

-- Move Santa according to a direction
move :: (Int, Int) -> Char -> (Int, Int)
move (x, y) c = case c of
  '^' -> (x, y + 1)
  'v' -> (x, y - 1)
  '>' -> (x + 1, y)
  '<' -> (x - 1, y)
  _   -> (x, y)

-- Count unique houses visited
santa :: String -> Int
santa path = S.size visited
  where
    (visited, _) = foldl step (S.singleton (0,0), (0,0)) path
    step (seen, pos) c =
      let next = move pos c
      in (S.insert next seen, next)


-- main
main :: IO ()
main = do
  contents <- readFile "./day03.txt"
  let firstLine = head (lines contents)
  print (santa firstLine)