Hi -
"countRects" seems like a bit of a leap. I think I understand "4 %~"
because you're overcounting by 4 rotations, but I don't comprehend the
magic behind "*/@(,>:)".
I see that "(,>:)" concatenates the shape to its increment, e.g. 2 3 3 4
for the input 2 3, but what's the rationale behind this?
Thanks,
Devon
On Tue, Oct 7, 2014 at 7:41 AM, Tikkanz <tikk...@gmail.com> wrote:
> Note that 200 x 200 is a bit of an overkill given 3x2 = 2x3
> The following choses the lower triangular of a matrix of the different
> sized rectangles to investigate.
> getSizes=: ,@(>:/~) # [: ,/ ,"0/~
> getSizes >: i. 5
>
> Given the sides of a rectangle you can count the number of rectangles as
> follows:
> countRects=: 4 %~ */@(, >:)
> countRects 2 3
>
> Now get the index of the rectangle size with a count closest to 2million
>
> idxClosest=: (i. <./)@(2e6 |@:- ])
>
>
> Putting it together
>
> */@({~ idxClosest@:(countRects"1)) getSizes >: i.200
>
>
>
> On Tue, Oct 7, 2014 at 5:37 PM, Jon Hough <jgho...@outlook.com> wrote:
>
> > Project Euler 85: https://projecteuler.net/problem=85
> > This problem is not really conceptually hard, but I am struggling with a
> J
> > solution.I have solved it in Python:
> > =============================================
> > def pe85(larg, rarg): count = 0 llist = range(1, larg+1)
> > rlist = range(1, rarg+1)
> > for l in llist: for r in rlist: count +=
> > l*r
> > return count
> >
> > if __name__ == "__main__": # test for 2x3 grid, as in question. k
> > = pe85(2,3) print "Test value: "+str(k) l1 = range(1,200) #
> > 200 lucky guess l2 = range(1,200) bestfit = 10000 # just a big
> > number area = 0 for i in l1: for j in l2:
> > diff = abs(2000000 - pe85(i,j)) if diff
> <
> > bestfit: area = i*j
> > bestfit = diff
> > print "AREA is "+str(area)
> >
> >
> > ================================================The above script will
> give
> > the final area of the closest fit to 2 million. (The python code may not
> be
> > the best). Also I tested all possibilities up to 200x200, which was
> chosen
> > arbitrarily(~ish).
> > Next my J. I go the inner calculation ok (i.e. see the function pe85
> > above). In J I have:
> > pe85 =: +/@:+/@:((>:@:i.@:[) *"(0 _) (>:@:i.@:]))
> > NB. I know, too brackety. Any tips for improvement appreciated.
> >
> >
> > But from here things get tricky. If I do the calculation over 200x200
> > possibilities I end up with a big matrix, of which I have to find the
> > closest value to 2 million, of which then I have to somehow get the (x,y)
> > values of and then find the area by x*y.
> >
> > The main issue is getting the (x,y) from the best fit value of the array.
> >
> > i.e. If I do pe85"(0)/~ 200, I get a big array, and I know I can get the
> > closest absolute value to 2 million but then I need to get the original
> > values to multiply together to give the best fit area. Actually I have
> > bumped into this issue many times. It is easy enough in a 1-d array,just
> do:
> > (I. somefunc ) { ])
> >
> > or similar to get the index. But for two indices the problem is beyond me
> > at the moment. Any help appreciated.Regards,Jon
> >
> >
> >
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> >
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
--
Devon McCormick, CFA
----------------------------------------------------------------------
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