From: Amos King <amos.l.king@...>
Date: 2007-04-19T00:35:14+09:00
Subject: Re: factorial in ruby

make it non-recursive  use

class Integer
  def fact
    return 1 if self == 0
    (1..self).inject { |i,j| i*j }
  end
end

Then you can just call
120.fact and that will return the factorial of 120 with no overflow.
You may want to add in a check for negatives

On 4/17/07, Gary Thomas <gthomas@takaro.co.nz> wrote:
> For large enough n it will also overflow the number. Probably the most
> efficient way would be to use a loop up to some (not very large) number, to
> use Stirling's approximation or its extension up to some larger number, and
> throw an overfow exception for anything larger than that.
>
> Cheers
>
> Gary Thomas
>
> > -----Original Message-----
> > From: David Simas [mailto:dsimas@imageworks.com]
> > Sent: Tuesday, 17 April 2007 6:58 a.m.
> > To: ruby-talk ML
> > Subject: Re: factorial in ruby
> >
> >
> > On Tue, Apr 17, 2007 at 02:56:16AM +0900, Jason Roelofs wrote:
> > > No and most likely not.
> > >
> > > def fact(n)
> > >  if n == 0
> > >    1
> > >  else
> > >    n * fact(n-1)
> > >  end
> > > end
> >
> > For large enough n, this will overflow the stack.  Since Ruby doesn't
> > optimize tail-recursive functions (and the above isn't tail recursive,
> > anyway), you'd better write this function as a loop (left as an exercise).
> >
> > DGS
> >
> > >
> > > Jason
> > >
> > > On 4/16/07, Trans <transfire@gmail.com> wrote:
> > > >
> > > >Is factorial defined anywhere in Ruby's core or standard library. If
> > > >not will it be in 1.9+?
> > > >
> > > >Thanks,
> > > >T.
> > > >
> > > >
> > > >
> >
> >
> >
>
>
>
>


-- 
Amos King
Ramped Media
USPS
Programmer/Analyst
St. Louis, MO
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