Re: [FWP] subexpr nearest the 'middle' of expr

[yanick1@sympatico.ca]

On Thu, Mar 08, 2001 at 11:37:57AM -0800, Jacob Carpenter wrote:
> Let's see a subroutine that takes three (3) arguments [expr, subexpr,
> replacement] -- call them whatever you like in the actual sub -- and returns
> "expr" with the "subexpr" nearest the middle (currently, I intend 'middle'
> to mean the byte position closest to half-the-byte-length of the string)
> replaced with "replacement". Subexpr should be a literal string. and should
> be centered on the middle, not begin in the middle -- i.e.
> &replace_mid('aaaaa', 'aaa', 'BBB') is to return 'aBBBa' not 'aaBBB'.
> 
> In the case that the same subexpr is found 'just-left-of-center' and
> 'just-right-of-center,' you have discretion in which your sub favors -- i.e.
> &replace_mid('aaaa', 'a', 'B') may return either 'aBaa' or 'aaBa'. I'd like
> to see some for each way.
> 
> I'm certain this will clearly illustrate that TMTOWTDI, and I'm looking
> forward to that. Ultimately, I have a feeling that this will result in a
> golf match, but initially, I'm just interested in seeing interesting ways of
> doing this.

I seems to recall there was a "regex in the middle" discussion, not so 
long ago. I think the final one-liner was substr'ing... Oh well, anyway,
here is my take at the problem:


sub replace_mid
{
my($s,$t,$r)=@_;my$l=length$s;1while$s!~
s/(.{$l,})$t(.{$l})/$1$r$2/&&--$l+1;$s;
}

It returns $expr unchanged if $subexpr is not present. It will also
choose the right-most $subexpr, but it can be trivially changed to
choose the left-most instead.


Joy,
Yanick


-- 
($_,$y)=("Yhre lo  .kePnarhtretcae\n",   '(.) (.)'  );
$y=~s/\(/(./gwhile s/$y/$2$1/xg;print;       @      !; 
                                     "     `---'    ";

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