[25886] in Perl-Users-Digest
Perl-Users Digest, Issue: 8114 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Wed May 25 11:05:22 2005
Date: Wed, 25 May 2005 08:05:06 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Wed, 25 May 2005 Volume: 10 Number: 8114
Today's topics:
網頁寄存服務計劃買十送二............................... dsafl@fald.com
Re: Fibonacci string <darkon.tdo@gmail.com>
Re: fibonacci string (Anno Siegel)
Re: fibonacci string <darkon.tdo@gmail.com>
Re: get the current week nbr <xx087@freenet.carleton.ca>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Wed, 25 May 2005 15:08:21 +0000 (UTC)
From: dsafl@fald.com
Subject: 網頁寄存服務計劃買十送二..................................
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------------------------------
Date: Wed, 25 May 2005 13:44:19 -0000
From: "David K. Wall" <darkon.tdo@gmail.com>
Subject: Re: Fibonacci string
Message-Id: <Xns9661631166E6Cdkwwashere@216.168.3.30>
John W. Krahn <someone@example.com> wrote:
> John W. Krahn wrote:
>> David K. Wall wrote:
>>
>>> Here's a fun fact I ran across in the book _The Golden Ratio_,
>>> by Mario Livio. Take the string '1' and replace it with '10'.
>>> Thereafter, replace any occurrence of '1' with '10' and '0' with
>>> '1'. Then count the number of 0s and 1s in the string. You get
>>> a Fibonacci sequence for each count (offset by one iteration).
>>>
>>> Here's Perl code to do it. You get about the same results if
>>> you start with '0', just offset a little.
>>>
>>> use strict;
>>> use warnings;
>>>
>>> my $v = '1';
>>> for (1 .. 20) {
>>> my ($n0, $n1) = (0, 0);
>>> $v = join '',
>>> map {
>>> if ($_) {
>>> $n1++;
>>> '10';
>>> }
>>> else {
>>> $n0++;
>>> '1';
>>> }
>>> } split //, $v;
>>> printf "%10d %10d\n", $n0, $n1;
>>> }
>>
>> You can make that shorter and faster:
>>
>> my $v = '1';
>> for ( 1 .. 20 ) {
>> printf "%10d %10d\n", $v =~ y/0//, $v =~ y/1//;
>> $v =~ s/([01])/ $1 ? '10' : '1' /eg;
>> }
>
> A bit faster. :-)
>
> my $v = '1';
> for ( 1 .. 20 ) {
> printf "%10d %10d\n", $v =~ y/0//, $v =~ y/1//;
> $v =~ s/./ $& ? '10' : '1' /eg;
>}
I bow to greater perl-fu, but with the caveat that I was more
interested in making the idea clear than in coming up with a fast
implementation. I'd accuse you of having too much time on your hands
if I weren't guilty of the same sort of thing myself.
------------------------------
Date: 25 May 2005 14:09:13 GMT
From: anno4000@lublin.zrz.tu-berlin.de (Anno Siegel)
Subject: Re: fibonacci string
Message-Id: <d720u9$bgl$1@mamenchi.zrz.TU-Berlin.DE>
Josef Moellers <josef.moellers@fujitsu-siemens.com> wrote in comp.lang.perl.misc:
> Anno Siegel wrote:
> > david k. wall <darkon.tdo@gmail.com> wrote in comp.lang.perl.misc:
> >
> >>here's a fun fact i ran across in the book _the golden ratio_, by
> >>mario livio. take the string '1' and replace it with '10'.
> >>thereafter, replace any occurrence of '1' with '10' and '0' with '1'.
> >>then count the number of 0s and 1s in the string. you get a
> >>fibonacci sequence for each count (offset by one iteration).
[...]
> > The observation that it doesn't matter where the zeroes and ones
> > appear in the strings leads to a solution that doesn't use s///:
> >
> > my $v = '1';
> > for ( 1 .. 20 ) {
> > my $n0 = $v =~ tr/0/1/;
> > printf "%10d %10d\n", $n0, length( $v) - $n0;
> > $v .= '0' x ( length( $v) - $n0);
> > }
> >
> > I generates a different sequence of strings $v (less fancy patterns),
> > but with the same distribution of ones and zeroes. If you prefer
> > to call it "cheating" I won't object.
>
> No, I'd call this professionalism.
Well, it's only a step away from generating the fibonacci numbers the
way they are defined and creating $v on the side:
my( $n0, $n1) = ( 0, 1);
for ( 1 .. 20 ) {
my $v = '1' x $n1 . '0' x $n0;
printf "%10d %10d\n", $n0, $n1;
( $n0, $n1) = ( $n1, $n0 + $n1);
}
That generates the same sequence $v as above, and it *would* be cheating.
It *is* dramatically faster (either way) than the s///-solutions we've seen.
These strings get large fast, and s/// does a lot of tail-copying for
all the size-changing replacements.
BTW, I have no idea how this subthread lost connection to the main thread
on the subject, at least for my newsreader.
Anno
------------------------------
Date: Wed, 25 May 2005 14:08:50 -0000
From: "David K. Wall" <darkon.tdo@gmail.com>
Subject: Re: fibonacci string
Message-Id: <Xns9661673947145dkwwashere@216.168.3.30>
Josef Moellers <josef.moellers@fujitsu-siemens.com> wrote:
> Anno Siegel wrote:
>
>> The observation that it doesn't matter where the zeroes and ones
>> appear in the strings leads to a solution that doesn't use s///:
>>
>> my $v = '1';
>> for ( 1 .. 20 ) {
>> my $n0 = $v =~ tr/0/1/;
>> printf "%10d %10d\n", $n0, length( $v) - $n0;
>> $v .= '0' x ( length( $v) - $n0);
>> }
>>
>> I generates a different sequence of strings $v (less fancy
>> patterns), but with the same distribution of ones and zeroes. If
>> you prefer to call it "cheating" I won't object.
>
> No, I'd call this professionalism.
> I wish I'd be as thorough as you.
>
> I bow my head,
Agreed. I just wanted to generate it so I could look at the pattern
for longer strings than the book contained.
The original string does have some interesting properties that do
depend on the order of the ones and zeroes. Some of them are
described at this URL:
http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/fibrab.html
The book I was reading mentions a few others.
Sorry, this is getting a bit removed from Perl.
------------------------------
Date: 25 May 2005 14:04:27 GMT
From: Glenn Jackman <xx087@freenet.carleton.ca>
Subject: Re: get the current week nbr
Message-Id: <slrnd991fc.lbs.xx087@smeagol.ncf.ca>
At 2005-05-25 08:06AM, Alexandre Jaquet <alexj@freesurf.ch> wrote:
> Hi again,
>
> Rigth now I'm looking for a function to get the current week nbr we are.
use POSIX 'strftime';
my $weekno = strftime '%V', localtime;
--
Glenn Jackman
NCF Sysadmin
glennj@ncf.ca
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
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Subject: Digest Administrivia (Last modified: 6 Apr 01)
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End of Perl-Users Digest V10 Issue 8114
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