Comments on: Factorial Challenge: Python, Perl, Ruby, and C

By: Help

Help — Mon, 10 Nov 2008 18:32:12 +0000

Hi, I’ve been desperately searching how to (in ruby) use the factorial in ruby, and as my friend only introduced me to ruby yesterday I was hoping you could explain to me, in dumbed down terms, how to use it. If not, could you tell me where to go to ask?
thanks
Andrew

By: acc

acc — Tue, 23 Jan 2007 17:33:48 +0000

Recursive version, equivalent to Ruby, is also fast, once you install the already mentioned package.

#!/usr/bin/perl -w
use strict;

use Math::BigInt lib => 'GMP';

use bignum;

sub fact
{
    my $n = $_[0];
    ( $n == 0 ) 
    ? 1
    : $n * fact( $n - 1 );
}

print fact( $ARGV[0] ), "\n"

By: acc

acc — Tue, 23 Jan 2007 17:24:00 +0000

Your Perl run was slow only because you didn’t actually use GMP library there: Perl “gracefully” fails to Perl-written implementation, when GMP is not installed. You should start your PPM (Perl Package Manager) and install Math::BigInt::GMP package. Then, Perl would be just as fast as C, for your starting example.

By: Brian

Brian — Sun, 17 Dec 2006 02:18:03 +0000

Here’s a version that’s a bit simpler and isn’t recursive:

class Fixnum
    def factorial
        (2..self).inject(1) { |product, i| product*i }
    end
end

It’s a bit easier to use to because you can just call it this way:
p 6.factorial

By: muyufan

muyufan — Sun, 01 Oct 2006 09:20:43 +0000

I just exec the factorial.py file

import time
start=time.clock()
def f(n):return reduce(lambda x,y:x*y,range(1,n+1))
f(n)
print "the time is :",time.clock()-start

in my 1.6G AMD(Duron) the result is:
40!: 0.0004 (s)
10000!: 0.22 (s)
100000!: 202 (s)

By: pjh

pjh — Tue, 27 Sep 2005 00:01:38 +0000

just for fun, the original ruby function can be replaced with:

def fact(n)
  n == 0 ? 1 : n * fact(n-1)
end

By: Patrick

Patrick — Mon, 22 Aug 2005 00:49:00 +0000

Adam (whose weblog requires I log in to leave comments directly) notices that python and ruby’s performance seem great while C is (naturally) very fast. Perl is in the mix, too, and he kindly doesn’t tear it apart though based on the numbers he would seem justified in doing so. I wondered if perl was realy that slow so I decided to take a look…