[Haskell-cafe] Project Euler: request for comments

[Oscar Picasso]

Daniel,

Thank you very much for your comments, there are very useful, indeed.
As a side note, my domain name is not oscarpicasso.com. It was already
taken by someone else so I decided to use opicasso.com

Oscar

On Sat, Aug 27, 2011 at 11:05 AM, Daniel Fischer
<daniel.is.fischer at googlemail.com> wrote:
> On Saturday 27 August 2011, 16:03:46, Oscar Picasso wrote:
>> Daniel,
>>
>> There are included as gists on the link provided. After your remark, I
>> looked at the generated html code in my blog. The gists are actually
>> displayed by running a javascript.
>> Maybe your browser settings don't allow to display them.
>
> NoScript :)
> I allowed oscarpicasso.com, but didn't look far enough to allow github.com.
>
>> On Sat, Aug 27, 2011 at 4:47 AM, Daniel Fischer
>>
>> <daniel.is.fischer at googlemail.com> wrote:
>> > On Saturday 27 August 2011, 02:34:24, Oscar Picasso wrote:
>> >> Hi,
>> >>
>> >> I order to improve my Haskell skills I started (again) to solve the
>> >> project euler problems with this language.
>> >> I am now at problem 11 and would really appreciate any comment about
>> >> my code in order to make it more elegant or efficient.
>
> In problem 11, by regarding all 4x4 subgrids separately, you recompute most
> of the horizontal and vertical products up to four times. Also you
> repeatedly use length and (!!). For a problem with such small parameters,
> it doesn't matter much, but consider a 1000x1000 grid with 100x100
> subgrids, it would really hurt then.
> You could get much better performance (and no worse code) by using an array
> for the grid.
>
> horizontalProd size grid row col
>    = product [grid!(row, col+i) | i <- [0 .. size-1]]
>
> verticalProd size grid row col
>    = product [grid!(row+i, col) | i <- [0 .. size-1]]
>
> seProd size grid row col
>    = product [grid!(row+i, col+i) | i <- [0 .. size-1]]
>
> neProd size grid row col
>    = product [grid!(row-i, col+i) | i <- [0 .. size-1]]
>
> maxProd size grid rows cols
>    = maximum $
>         [horizontalProd size grid row col
>             | row <- [0 .. rows-1], col <- [0 .. cols-size]]
>      ++ [verticalProd size grid row col
>             | col <- [0 .. cols-1], row <- [0 .. rows-size]]
>      ++ [seProd size grid row col
>             | row <- [0 .. rows-size], col <- [0 .. cols-size]]
>      ++ [neProd size grid row col
>             | row <- [size-1 .. rows-1], col <- [0 .. cols-size]]
>
>
>
> Another thing,
>
> slice n = takeWhile ((n ==) . length) . map (take n) . tails
>
> if you also import tails from Data.List.
>
> Concerning the newly posted problem 12: Yes, it would be much faster to
> count the divisors using the prime factorisation (plus, there's another
> speedup available if you go that route).
>
>> >
>> > I don't see any code, where would I have to look?
>> >
>> >> My solutions can be found here:
>> >> http://fp.opicasso.com/tag/projecteuler
>> >>
>> >> Oscar Picasso
>
>