From: Gennady <gfb@...>
Date: 2004-08-04T10:19:53+09:00
Subject: Re: Fastest way to reverse-process a string?

Ara.T.Howard wrote:
> On Wed, 4 Aug 2004, Lloyd Zusman wrote:
> 
>> In a ruby program I'm writing, I want to parse a string in reverse and
>> feed each of its individual characters through a state machine.
>>
>> A "hammer and tongs" solution looks like this:
>>
>>  string.reverse.split(//).each {
>>    |ch|
>>    feedIntoStateMachine(ch)
>>  }
>>
>> However, this seems rather inefficient.  Does anyone know of a faster
>> algorithm for this in ruby?
>>
>> Thanks in advance.
>>
>>
>> -- 
>> Lloyd Zusman
>> ljz@asfast.com
>> God bless you.
> 
> 
> ~ > ruby -e 's="raboof"; (s.size - 1).downto(0){|i| print s[i].chr}; puts'
> foobar
> 

If you add this as a fourth benchmark

   x.report("4") {
     size = str.size - 1
     100000.times {
       size.downto(0) { |_index|
         str[_index].chr
       }
     }
   }

The result will be:
              user     system      total        real
1        2.630000   0.000000   2.630000 (  2.627852)
2        2.660000   0.000000   2.660000 (  2.659415)
3        1.600000   0.000000   1.600000 (  1.597412)
4        1.840000   0.000000   1.840000 (  1.845511)

So this algorithm is next to the fastest one based on each_byte.

Gennady.

> 
> -a
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