adventofcode/2022/app/Day8/Main.hs

module Day8.Main (main) where

import System.IO
import Data.List

main :: IO ()
main = do
    putStrLn "Day 8"
    
    handle <- openFile "app/Day8/input" ReadMode
    contents <- hGetContents handle

    let r1 = part1 contents
    putStrLn $ "part 1: " ++ show r1

    let r2 = part2 contents
    putStrLn $ "part 2: " ++ show r2

type Tree = (Int,[Int],[Int],[Int],[Int]) -- Self, N, E, S, W

enumerate :: [a] -> [(Int, a)]
enumerate = zip [0..]

parseData :: String -> [[Int]]
parseData contents = (map . map) (read . singleton :: Char -> Int) $ lines contents

toTrees :: [[Int]] -> [Tree]
toTrees rows = [(tree, north r c, east r c, south r c, west r c) | (r, line) <- enumerate rows, (c, tree) <- enumerate line]
    where
        columns = transpose rows
        east r c = drop (c + 1) $ rows !! r
        west r c = reverse $ take c $ rows !! r
        north r c = reverse $ take r $ columns !! c
        south r c = drop (r + 1) $ columns !! c

isVisible :: Int -> [Int] -> Bool
isVisible _ [] = True
isVisible t ts = all (< t) ts

invisibleFromOutside :: Tree -> Bool
invisibleFromOutside (t,n,e,s,w) = all (not . isVisible t) [n,e,s,w]

part1 :: String -> Int
part1 = length . filter (not . invisibleFromOutside) . toTrees . parseData

-- Includive version of takeWhile (because lentgh takeWhile + 1 doesn't work for when the outer border is the reason you can't see further)
takeWhileI :: (a -> Bool) -> [a] -> [a]
takeWhileI _ [] = []
takeWhileI p (x:xs) =
  x : if p x then takeWhileI p xs else []

viewingDistance :: Int -> [Int] -> Int
viewingDistance t ts = length $ takeWhileI (< t) ts

scenicScore :: Tree -> Int
scenicScore (t,n,e,s,w) = product $ map (viewingDistance t) [n,e,s,w]

part2 :: String -> Int
part2 = maximum . map scenicScore . toTrees . parseData