From: Rob Biedenharn <Rob@...>
Date: 2008-05-03T01:44:21+09:00
Subject: Re: [QUIZ] Reverse Divisible Numbers (#161)


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/

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