On Sun, Feb 24, 2013 at 12:15:05AM +0100, Emanuel Koczwara wrote:
Hi,
Dnia 2013-02-23, sob o godzinie 17:35 -0500, Brent Yorgey pisze:
On Sat, Feb 23, 2013 at 04:39:53PM +0100, Emanuel Koczwara wrote:
Hi,
Note: Following code is a solution for a problem from hackerrank.com (Category: Artifical Intelligence / Single Player Games / Bot saves princess).
Looks pretty good overall. One note is that using lists of lists for Grid and Heuristic will be slow, especially Heuristic since you do lots of repeated lookups. For small grids it really doesn't make much difference, but if you wanted to run it on larger grids you might notice. Since both the Grid and Heuristic values are created once and then used in a read-only fasion, this is a perfect opportunity to use arrays: see
http://hackage.haskell.org/packages/archive/array/latest/doc/html/Data-Array...
Using read-only arrays is really quite simple (as opposed to read/write arrays which require a monad of some sort).
Thank you, I will try Arrays. Handling list of lists is very hard for me. Please look at this code: http://hpaste.org/82925 (indexedGrid and getDirty). In C/C++ it's very natural for me, here it looks like i'm missing something.
In C/C++ you get to use arrays with indexing. Lists are entirely different, so it's no surprise that something natural in C/C++ should feel foreign here. Indeed, I don't think lists are the right data structure for you to be using. If you use arrays I think this code will become much simpler too. A good rule of thumb is that lists should be primarily used as a *control structure* (i.e. to describe something that would be done with a loop in an imperative language). If you find yourself using lists as a *data structure*, especially a random-access one, you probably ought to be using something else instead (Data.Sequence, arrays, ...) -Brent