Oops,
biggap=:{~0 1+[:(i.<./)2-/\]
Thanks,
--
Raul
On Sunday, September 17, 2017, Erling Hellenäs <erl...@erlinghellenas.se>
wrote:
> Strange things happen here. It works but give incorrect results. I just
> changed F to lower case to put it through my tests. Not sure what might
> happen here. I have J 8.04 on this machine. 64 bit.
> I never doubted that p: was good. I just thought that since it was a Quora
> challenge that using p: would not be a good idea, since the algorithm used
> in p: is not known to the audience. It also seemed like some kind of
> cheating, like using a subroutine someone else wrote to solve half the
> problem.
> Well, I also thought p: would have to generate the array of primes for
> each call, but it's obviously not the case. There is a formula which does
> the trick? Or a hash table of primes?
>
> thru=: <. + >:@>. i.@- <.
>
> biggap=: {~ 0 1 - [: (i. <./) 2 -/\ ]
>
> f=: [: thru/ 1 _1 + [: biggap <./ >. >./ <. thru&.(p:inv)
>
> s=: 10 f 100
>
> s
>
> 20 21 22
>
> >./90 91 92 93 94 95 96 = s
>
> |length error: scriptd
>
> | >./90 91 92 93 94 95 96 =s
>
> |[-5] j:\j64-803-user\projects\quoraraul.ijs
>
> inv
>
> ^:_1
>
>
> Cheers,
>
> Erling
>
> On 2017-09-17 17:38, Raul Miller wrote:
>
>> Yes. :)
>>
>> When J provides a mechanism for something it is usually worth trying.
>> Sometimes you can write something faster, but usually J's approach
>> will be useful.
>>
>> For example, in this case, consider this approach:
>>
>> thru=: <. + >:@>. i.@- <.
>> biggap=: {~ 0 1 - [: (i. <./) 2 -/\ ]
>> F=: [: thru/ 1 _1 + [: biggap <./ >. >./ <. thru&.(p:inv)
>>
>> There will be cases where another approach could be more efficient,
>> but it performs reasonably well.
>>
>> Thanks,
>>
>>
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