Advent of Code 2021
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{-# LANGUAGE TupleSections #-}
module Day5_1 where
import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
import Data.Text (splitOn, unpack, pack)
import Prelude hiding (splitAt)
import Data.List (sort, intersect)
import Data.Bifunctor (bimap)
type Coordinate = (Int, Int)
type Range = ([Int], [Int])
toCoord :: String -> Coordinate
toCoord str = (x, y)
where
xy = splitAt "," str
x = read $ head xy
y = read $ xy !! 1
isStraight :: Coordinate -> Coordinate -> Bool
isStraight c1 c2 = fst c1 == fst c2 || snd c1 == snd c2
splitAt :: String -> String -> [String]
splitAt delimiter str = map unpack $ splitOn (pack delimiter) $ pack str
range :: (Num a, Enum a, Eq a) => a -> a -> [a]
range a b
| a == b = [a]
| otherwise = [a, a + signum (b - a) .. b]
coordsToRange :: (Coordinate, Coordinate) -> Range
coordsToRange (a, b) = bimap (range (fst a)) (range (snd a)) b
points :: (Range, Bool) -> [Coordinate]
points (range, diag)
| diag = uncurry zip range
| otherwise = [ (i,j) | i <- fst range, j <- snd range ]
intersections :: [(Range, Bool)] -> [[Coordinate]]
intersections [] = []
intersections (x:xs) = map (\y -> points x `intersect` points y) xs ++ intersections xs
dedup :: Eq a => [(a, a)] -> [(a, a)]
dedup [] = []
dedup (x:xs) = x : dedup (filter (x /=) xs)
main :: IO ()
main = do
input <- openFile "inputs/5.txt" ReadMode
contents <- hGetContents input
let coords = map toCoord . splitAt " -> " <$> lines contents
-- remove lines that aren't horizontal/vertical and sort them
let straight' = map sort $ filter (\(x:y:_) -> isStraight x y) coords
let gay' = filter (\(x:y:_) -> not $ isStraight x y) coords
let straight = map ((, False) . coordsToRange . (\x -> (head x, x !! 1))) straight'
let gay = map ((, True) . coordsToRange . (\x -> (head x, x !! 1))) gay'
print . length . dedup . concat $ intersections $ straight ++ gay
hClose input