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import Data.List
type Pr = (Int, Int)
(!?) :: [[a]] -> Pr -> Maybe a
grid !? (row, col)
| row < 0 = Nothing
| row >= length grid = Nothing
| col < 0 = Nothing
| col >= (length $ head grid) = Nothing
| otherwise = Just (grid !! row !! col)
findChs1 :: Char -> String -> Int -> Int -> [Pr] -> [Pr]
findChs1 _ [] _ _ acc = acc
findChs1 ch (h:t) j i acc
| ch == h = findChs1 ch t j (i + 1) (acc ++ [(j,i)])
| otherwise = findChs1 ch t j (i + 1) acc
findChs :: Char -> [String] -> Int -> [Pr] -> [Pr]
findChs _ [] _ acc = acc
findChs ch (h:t) j acc = findChs ch t (j + 1) (acc ++ findChs1 ch h j 0 [])
checkCh :: Char -> [String] -> Pr -> Pr -> [(Pr, Pr)]
checkCh ch grid coo@(row, col) dir@(dr, dc)
| grid !? (row + dr, col + dc) == Just ch = [(coo, dir)]
| otherwise = []
findMCorners :: [String] -> Pr -> [(Pr, Pr)]
findMCorners grid coo =
let checkM = checkCh 'M' grid coo in
checkM (-1, -1) ++
checkM (-1, 1) ++
checkM ( 1, -1) ++
checkM ( 1, 1)
findMNeighs :: [String] -> Pr -> [(Pr, Pr)]
findMNeighs grid coo =
let checkM = checkCh 'M' grid coo in
findMCorners grid coo ++
checkM (-1, 0) ++
checkM ( 0, -1) ++
checkM ( 0, 1) ++
checkM ( 1, 0)
testXmas :: [String] -> (Pr, Pr) -> Bool
testXmas grid ((row, col), (dr, dc)) =
grid !? (row + 2 * dr, col + 2 * dc) == Just 'A' &&
grid !? (row + 3 * dr, col + 3 * dc) == Just 'S'
testMas :: [String] -> (Pr, Pr) -> Bool
testMas grid ((row, col), (dr, dc)) =
grid !? (row - dr, col - dc) == Just 'S'
car :: (a, a) -> a
car (a, _) = a
findReps :: [Pr] -> [Pr] -> [Pr]
findReps acc [] = acc
findReps acc (h:t)
| h `elem` t = findReps (h:acc) t
| otherwise = findReps acc t
part1 grid =
length $ filter (testXmas grid) $
concat $ map (findMNeighs grid) $
findChs 'X' grid 0 []
part2 grid =
length $ findReps [] $
map (car) $ filter (testMas grid) $
concat $ map (findMCorners grid) $
findChs 'A' grid 0 []
main = do
file <- readFile "day04.input"
let lns = lines file
putStrLn ("Part 1: " ++ (show $ part1 lns))
putStrLn ("Part 2: " ++ (show $ part2 lns))
|
