From: Shane Emmons <semmons99@...>
Date: 2008-05-03T02:26:43+09:00
Subject: Re: [QUIZ] Reverse Divisible Numbers (#161)

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On Fri, May 2, 2008 at 12:44 PM, Rob Biedenharn <Rob@agileconsultingllc.com>
wrote:

>
> On May 2, 2008, at 12:10 PM, Ken Bloom wrote:
>
>  On Fri, 02 May 2008 10:28:00 -0500, Matthew Moss wrote:
> >
> > > Quiz #161
> > > Reverse Divisible Numbers
> > >
> > > This week's quiz is borrowed from Jon Galloway
> > > (http://tinyurl.com/5jvf37).
> > > Don't read the comments or solution there without trying this first!
> > >
> > > Your task is to write a bit of Ruby code that will find and report all
> > > integers that are divisible by their reverse. For example, 9801 is
> > > divisible by 1089.
> > >
> > > Your script should accept a single, optional argument to specify the
> > > upper
> > > limit of your search. If not provided, the default should be one
> > > million.
> > >
> > > There are two extra rules for finding these "reverse divisible"
> > > numbers:
> > >
> > > 1. Don't count palindromes; they are obviously reverse-divisible. 2.
> > > Don't count numbers ending with zero. Reversing such numbers forces
> > > you
> > >  to drop leading zeros on the divisor, and that's not as much fun.
> > >
> >
> > Here's what I've found:
> >
> > 1089 * 9 = 9801
> > 2178 * 4 = 8712
> > 10989 * 9 = 98901
> > 21978 * 4 = 87912
> > 109989 * 9 = 989901
> > 219978 * 4 = 879912
> >
> > real    0m55.234s
> > user    0m53.995s
> > sys     0m0.012s
> >
> > --Ken
> >
> > --
> > Ken (Chanoch) Bloom. PhD candidate. Linguistic Cognition Laboratory.
> > Department of Computer Science. Illinois Institute of Technology.
> > http://www.iit.edu/~kbloom1/ <http://www.iit.edu/%7Ekbloom1/>
> >
>
> 2178 * 4 = 8712
> 1089 * 9 = 9801
> 21978 * 4 = 87912
> 10989 * 9 = 98901
> 219978 * 4 = 879912
> 109989 * 9 = 989901
>
> real    0m13.113s
> user    0m12.411s
> sys     0m0.081s
>
> While I find them in a slightly different order, I'm surprised by the 4x
> speedup.  I wonder if there's a better way to post comparisons that would
> negate machine differences and focus on algorithmic distinctions without
> posting code?
>
> -Rob
>
> Rob Biedenharn          http://agileconsultingllc.com
> Rob@AgileConsultingLLC.com
>
>
>
H:\personal\RubyQuiz>ptime quiz161.rb

ptime 1.0 for Win32, Freeware - http://www.pc-tools.net/
Copyright(C) 2002, Jem Berkes <jberkes@pc-tools.net>

=== quiz161.rb ===
8712
9801
87912
98901
879912
989901

Execution time: 7.691 s

-- 
Shane Emmons
E: semmons99@gmail.com

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