[Haskell-beginners] Searching for word in 2D array

[Lorenzo Bolla]

On Thu, Mar 22, 2012 at 5:45 PM, Nathan Hüsken <nathan.huesken at posteo.de>wrote:

> Hey,
>
> I have the following problem. I have an 2D array of letters, like this:
>
> b w y l
> a i l q
> h w r a
> o q e d
>
> Now I am searching for all occurrences of a specific word in this
> array. The word can be horizontal, vertical or diagonal, like "bird"
> is in the example above. I am a beginer at haskell and I do not know
> where to start ...
>
> OK, I would represent the word as an String == [Char] and my array as
> [[Char]] (or would some kind of fixed size array make more sense?).
>
> In an imperative program, I would just search for the first letter and
> than check the rest of the word in all directions.
> If I do this, I need direct indexing of the array.
>
> Any advise in which direction to think?
>
>
What about using Vector (for fast indexing and slicing) and use a 1D array?
Maybe something as simple as this?

import Data.Vector hiding (elem)
import Prelude hiding (length)

ncols :: Int
ncols = 4

row :: Int -> Vector a -> Vector a
row i = slice (i * ncols) ncols

col :: Int -> Vector a -> Vector a
col i v = let idxs = [i, i + ncols .. length v]
            in ifilter (\i _ -> i `elem` idxs) v

diag :: Int -> Vector a -> Vector a
diag i v = let idxs = [i, i + ncols + 1 .. length v]
            in ifilter (\i _ -> i `elem` idxs) v

v :: Vector Char
v = fromList "bwylailqhwraoqed"

main :: IO ()
main = do
        print v
        print $ row 0 v
        print $ col 0 v
        print $ diag 0 v


L.






> Thanks!
> Nathan
>
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