From: Simon Conrad-Armes <curne@...> (Curne)
Date: 2004-11-06T23:23:11+09:00
Subject: Re: Succ distance between two strings


On Nov 6, 2004, at 3:07 PM, David A. Black wrote:

> Hi --
>
> On Sat, 6 Nov 2004, trans.  (T. Onoma) wrote:
>
>>
>> Is there an efficient way to calculate the "succ distance" between 
>> two strings
>> (without iterating over each succession)? Examples:
>>
>>   'a'..'a'    0
>>   'a'..'b'    1
>>   'a'..'z'    25
>>   'a'..'aa'   26
>
> 'a'...'aa'.to_a.size   # would be one way

That still iterates over all elements but it looks sweet :)
Only for large strings would be a problem


My stab:

def diff_succ s1, s2
   t1 = t2 = 0
   s1.each_byte{|c| t1 = t1*26 + c - 96}
   s2.each_byte{|c| t2 = t2*26 + c - 96}
   t2 - t1
end

def t s1, s2
   puts "#{s1}..#{s2}  => #{diff_succ s1, s2}"
end

t 'a', 'a'    #0
t 'a', 'b'    #1
t 'a', 'z'    #25
t 'a', 'aa'   #26

t 'A', 'B'
t 'A', 'Z'
t 'A', 'AA'


output:
a..a  => 0
a..b  => 1
a..z  => 25
a..aa  => 26
A..B  => 1
A..Z  => 25
A..AA  => -806


Notice how it breaks on multi-letter uppercase strings? that is because 
of the -96. Maybe one should just lowercase the args...

/Curne
--
Mailing lists confuse me. Often I don't recognize my own posts and set 
about writing a flaming reply where I violently disagree. 
[curne@curnomatic.dk]