Actuary the use of ravel and antibase is common practice to solve certain problems in APL and isn't considered cheating. So I wouldn't say it's "not nice" but I would definitely go for antibase instead of a combination of floored-divide and modulus. As a bonus, a solution based on antibase would scale to problems of any rank and not just 2d matrices.
Have fun! -- Stefano > On 10/ott/2014, at 17:35, Sebastiano Tronto <sebastiano.tro...@gmail.com> > wrote: > > Hi, > A dirty trick to get the job done would be to ravel the matrix ( , ), solve > the 1d version of the problem and then get the "true" indexes with > something like (<.@%&200 , 200&|). > For example, if you needed to just find the max: > (<.@%&200 , 200&|) (i. >./) , m > where m is your matrix. > > I know this isn't a nice way to solve the problem, but it should work. > > Sebastiano > > 2014-10-07 6:37 GMT+02:00 Jon Hough <jgho...@outlook.com>: > >> 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 ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
