[Jprogramming] Project Euler

['Mike Day' via Programming]

Had a new look at the problem.  Reworked verbs as I'd not kept the 
old.  First pass,  pretty brutal,  took ~100 sec,  in j806beta with avx. 
Later efforts to speed it up were worse!  Evidently better to compare 
sorted character reps of numbers than sorted base 10 decodes.

M

Please reply to mike_liz.day at tiscali.co.uk.      
Sent from my iPad

> On 15 Mar 2017, at 07:48, 'Mike Day' via Programming <programming at jsoftware.com> wrote:
> 
> Only just up - having breakfast!  I evidently solved it,  as the project's discussion thread
> is open to me,  but I don't have a record of my method.
> 
> Early-ish PE problems were amenable to brute force,  and I expect that's how I would have
> done it.
> 
> AFAIrecall, later problems involving phi require insight how phi is calculated:
> 
>   if n = */p^q,         phi(n) = */(p^(q-1)) * p-1
> eg
>    q:360
> 2 2 2 3 3 5
>    p =: 2 3 5
>    q =: 3 2 1
> 
>   */(p^q-1) * p-1
> 96
> 
>   5 p: 360
> 96
> 
> so n/phi(n) is
>   */@:(%<:) p
> 3.75
> 
> No time for more - away from wifi for 10 hours or so!
> Mike
> 
> 
> 
>> On 15/03/2017 03:09, Don Guinn wrote:
>> My second approach was brute force like you did. It gave the same number as
>> my first approach. And interestingly it was faster than my first approach.
>> Happens sometimes. The only thing I can think of is that I found the answer
>> but I didn't supply what they wanted. I supplied the first number that had
>> as a permutation of the digits given sorted by (%totient)n . I cheated.
>> Stole totient from J phrases.
>> 
>> The only thing I can think of is that they wanted something other than the
>> n that I found.
>> 
>> On Tue, Mar 14, 2017 at 8:12 PM, 'Jon Hough' via Programming <
>> programming at jsoftware.com> wrote:
>> 
>>> I just tried it and got the right answer. But my approach is essentially
>>> brute force:
>>> I basically stringified  (":) the totient result, sorted it, and compared
>>> to the sorted stringified original number.
>>> 
>>> I can be more specific if you like.
>>> 
>>> Regards,
>>> Jon
>>> --------------------------------------------
>>> On Wed, 3/15/17, Don Guinn <donguinn at gmail.com> wrote:
>>> 
>>>  Subject: [Jprogramming] Project Euler
>>>  To: "Programming forum" <programming at jsoftware.com>
>>>  Date: Wednesday, March 15, 2017, 9:37 AM
>>> 
>>>  Has anyone out there solved problem
>>>  70? I have worked it two ways which
>>>  give the same answer but it is given as incorrect. I don't
>>>  want to divulge
>>>  what I did as that is against their rules. I must be missing
>>>  something and
>>>  presenting the wrong number for the result. Or is it
>>>  possible that their
>>>  answer is wrong?
>>> 
>>>  Glad to discuss it in the forum, but if anyone wants to
>>>  contact me
>>>  privately so we don't break Project Euler rules, contact me
>>>  at
>>>  donguinn at gmail.com
>>> 
>>>  Thanks.
>>>  ----------------------------------------------------------------------
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> 
> 
> 
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