Lazy evaluation won't help you cut the processing time, but it does reduce the memory footprint to practically null, and the lambda calculus involved opens the possibility for further optimisations. I guess I don't like having to think about optimizing my J code (if it makes it any less readable), and perhaps I'm overestimating the interpreter's opportunities for optimizing heavy brute force algorithms like this one.
________________________________ From: Programming <programming-boun...@forums.jsoftware.com> on behalf of 'Pascal Jasmin' via Programming <programm...@jsoftware.com> Sent: Sunday, May 20, 2018 1:06:09 AM To: programm...@jsoftware.com Subject: Re: [Jprogramming] Quora Problem This is more math, than eager/lazy evaluation issue. Though if lazy (programmer), you might use solution for 10 and 100 to guess at 1M. It's an extention of unique pairs that add up to a sum. <.@-: sum The extention is a matter of avoiding duplicates while summing to 1M less the largest of the triplets, for eacch "largest triplet" ________________________________ From: Henry Rich <henryhr...@gmail.com> To: programm...@jsoftware.com Sent: Saturday, May 19, 2018 6:41 PM Subject: Re: [Jprogramming] Quora Problem I don't think it's the interpreter's strategy that is at fault. odo 3#1e6 is asking the machine to create a set of 1e18 triplets, which you will then presumably check to see if they add to 1e6, and then cast out duplicates. If somehow the interpreter could feed you the 1e18 values one at a time, you still wouldn't get to a solution. A better strategy is to read about partitions and generating functions thereof. Henry Rich On 5/19/2018 5:58 PM, james faure wrote: > This is a good example of a very annoying limitation of the current > interpreter's eager evaluation strategy, in this case one is forced to come > up with some sort of non-idiomatic iterative 'hack' to get a result. > Concretely, I guess you're forced to use an accumulator with ^: or an > explicit loop, which hurts. > > ________________________________ > From: Programming <programming-boun...@forums.jsoftware.com> on behalf of > Skip Cave <s...@caveconsulting.com> > Sent: Saturday, May 19, 2018 10:43 PM > To: programm...@jsoftware.com > Subject: [Jprogramming] Quora Problem > > Another interesting quora problem: > > How many distinct triplets have a sum of 1,000,000 (provided all numbers > are integers and are positive)? > <https://www.quora.com/qemail/track_click?al_imp=eyJ0eXBlIjogMzUsICJoYXNoIjogMTcxMDQ0NjU4Mn0%3D&al_pri=QuestionLinkClickthrough&aoid=oMo937UDzj8&aoty=2&aty=4&click_pos=1&ct=1526747413834671&et=103&id=62216bf7b30d40aea1d79bf4401c8317&request_id=289&src=1&st=1526747413838426&stories=2518686273&uid=bqluVqSeN78&v=0> > > The obvious straightforward solution would be to use the odometer verb: > > odo=: #: i.@(*/) > > 1e6=+/"1 odo 3#1e6 > > |limit error: odo > > | 1000000=+/"1 odo 3#1000000 > > > Ooops. Unfortunately, I don't have near enough memory to use this approach. > > Any suggestions? > > > Skip > > > > Skip Cave > Cave Consulting LLC > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm --- This email has been checked for viruses by AVG. http://www.avg.com ---------------------------------------------------------------------- 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
