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import Data.Char
import Data.List
import Data.Maybe
type Height = Int
type Coo = (Int, Int)
type Map = [[Height]]
data Trail = Point Coo Height Trail | Nowhere deriving Show
(!?) :: [[a]] -> Coo -> Maybe a
mp !? (row, col)
| row < 0 = Nothing
| row >= length mp = Nothing
| col < 0 = Nothing
| col >= (length $ head mp) = Nothing
| otherwise = Just (mp !! row !! col)
consume :: [Char] -> Map
consume file =
map (map (digitToInt)) $ lines file
trailheads2 :: [Coo] -> Int -> Int -> [Height] -> [Coo]
trailheads2 acc _ _ [] =
reverse acc
trailheads2 acc r c (h:rest)
| h == 0 = trailheads2 ((r, c):acc) r (c + 1) rest
| otherwise = trailheads2 acc r (c + 1) rest
trailheads1 :: [Coo] -> Int -> Map -> [Coo]
trailheads1 acc _ [] =
acc
trailheads1 acc r (row:rest) =
trailheads1 (acc ++ heads) (r + 1) rest
where heads = trailheads2 [] r 0 row
trailheads :: Map -> [Coo]
trailheads = trailheads1 [] 0
trails2 :: Map -> Trail -> [Trail]
trails2 mp p@(Point (r,c) h _) =
map pointify $
catMaybes $
map oneup
[nxt (-1, 0), nxt (0, -1), nxt (0, 1), nxt (1, 0)]
where
pointify c = Point c (h+1) p
oneup (nr, nc, Just nh) = if nh == h + 1 then Just (nr, nc) else Nothing
oneup (_, _, Nothing) = Nothing
nxt (dr, dc) = (r+dr, c+dc, mp !? (r+dr, c+dc))
trails1 :: Map -> [Trail] -> [Trail] -> [Trail]
trails1 _ acc@((Point _ 9 _):_) [] =
acc
trails1 mp acc [] =
trails1 mp [] acc
trails1 mp acc (th@(Point _ 9 _):rest) =
trails1 mp (th:acc) rest
trails1 mp acc (th:rest) =
trails1 mp (acc ++ trails2 mp th) rest
trails :: Map -> Coo -> [Trail]
trails mp th =
trails1 mp [] [Point th 0 Nowhere]
score :: [Trail] -> Int
score th =
length $ nub $ map untrail th
where
untrail (Point c _ _) = c
part1 :: Map -> Int
part1 mp =
sum $ map (score . (trails mp)) $ trailheads mp
main = do
file <- readFile "day10.input"
let mp = consume file
putStrLn ("Part 1: " ++ (show $ part1 mp))
--putStrLn ("Part 2: " ++ (show $ part2 mp))
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