🚀 go-pugleaf

In article <wzenrwg142.fsf@stego.cs.ruu.nl>, piet@stego.cs.ruu.nl wrote:
|>>>>> thecrow@iconn.net (The Crow) (TC) writes:
|
|TC> Here is what I am trying to do, I want to find the last NON-ZERO digit
|TC> of a given factorial. For instance,
|
|TC> 5! = 120
|
|TC> so the last non-zero digit is 2. I want to be able to do this up to
|TC> 1000. Problem is, no matter how huge of a data-type you use, there
|TC> isn't any way for the computer to handle 1000!, it is however possible

|A little thinking before coding solves this problem very easily:
|
|Let N be then number whose factorial you are considering.
|
|What you want is the number of trailing zeroes + 1. 

[ clever solution of not-the-posters-problem deleted ... ]

No, that's not what he wanted. A little reading before thinking before
coding may come in handy sometimes ;-) What the original poster wants
is the value of the rightmost non-zero digit of n!. 

Let D(n) be the value of the rightmost non-zero digit of number n,
it is easy to show that D(n!)= D(D(n)*D((n-1)!). Here's function D,
written in C (it still is c.l.c isn't it?)

int D(n) {

	while (n && !(n%10))
		n/= 10;


	return n%10;
}

I leave the rest of the program as an exercise for the reader (boy,
I still love writing that ;-)

kind regards,

Jos aka jos@and.nl
-- 
Atnwgqkrl gy zit vgksr, ug qshiqwtzoeqs!