From: Alan Malloy <vandraeza@...>
Date: 2012-02-18T01:41:07+09:00
Subject: Re: Factorial

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This method isn't as fast as using Math.gamma, but I believe any reasonable
factorial can be calculated.

A factorial of 10,000 benchmarked at 0.121007 seconds using this approach,
where 100,000 took 14.354879 seconds.

(1..n).inject(:*)

On Fri, Feb 17, 2012 at 8:55 AM, Tanaka Akira <akr@fsij.org> wrote:

> 2012/2/17 Junayeed Ahnaf Nirjhor <zombiegenerator@aol.com>:
> >
> > What is the most efficient way in Ruby to calculate the factorial of any
> > given sum? Is there any way to make it as fast as in C?
> >
> > Complexity doesn't matter as long as it works correctly.
>
> How about Math.gamma(n+1).to_i for fact(n) assuming n <= 22 ?
>
> If the restriction, n <= 22 is not acceptable,
> table lookup is another option.
>
> I think C is not so useful here because fact(21) overflows 64bit signed
> int.
> --
> Tanaka Akira
>
>

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