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
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