countisland.hs

import qualified Data.Vector as V
import Data.Maybe

data IsNew = N|O deriving (Show)
data Cell = Cell Int Int IsNew deriving (Show)

instance Eq  Cell where
    (==) (Cell x0 y0 _) (Cell x1 y1 _) = x0 == x1 && y0 == y1


ltoV::[a]-> V.Vector a
ltoV = V.fromList

conv::String -> V.Vector Int
conv = ltoV . map (read::String -> Int) . words

countIsland :: V.Vector (V.Vector Int) -> [Cell]
countIsland island = islandhelper1 (0, 0) []
    where
        islandhelper1::(Int, Int) -> [Cell] -> [Cell]
        islandhelper1 a@(x, y) g = case island V.!? x of
                                      Just row -> islandhelper2 row a g
                                      _ -> g
        islandhelper2:: V.Vector Int -> (Int, Int) -> [Cell] -> [Cell]
        islandhelper2 xss (x, y) g = case xss V.!? y of
                                          Just 1 -> islandhelper2 xss (x, y+ 1) (Cell x y O:g)
                                          Just 0 -> islandhelper2 xss (x, y+1) g
                                          _ -> islandhelper1 (x+ 1, 0) g

removeNbs:: [Cell] -> [Cell]
removeNbs [] = []
removeNbs (x:xss) = removeNbs1 [x] xss
    where
        removeNbs1 :: [Cell]->[Cell] -> [Cell]
        removeNbs1 [] g = g
        removeNbs1 (x:xss) g = let acc = (merge fm xss) in removeNbs1 acc (filter (==x) g)
            where
                fm :: [Cell]
                fm = mapMaybe getnbs [(0,1), (1,0), (0, -1), (-1, 0)]
                getnbs ::(Int, Int) -> Maybe Cell
                getnbs (x, y) = if Cell x y O `elem` g then Just (Cell x y O) else Nothing


merge :: [Cell] -> [Cell] -> [Cell]
merge [] g = g
merge g [] = g
merge (x:xss) y = merge (x:y) xss



main::IO()
main = do
    content <- ltoV . map conv . lines <$> readFile "input.txt"
    print . removeNbs . countIsland $ content