NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part1/8207

Text File | 1996-08-05 | 2.0 KB | 50 lines

Path: sun001.spd.dsccc.com!spd!jmccarty
From: [e-mail] (Mike McCarty)
Newsgroups: comp.lang.pascal.misc,comp.lang.c++,comp.lang.c,comp.lang.pascal.borland
Subject: Re: Tough FACTORIAL math problem...
Date: 15 Feb 1996 19:15:26 GMT
Organization: DSC Communications Corporation, Plano, Texas USA
Message-ID: <4g00oe$[e-mail]>
References: <4fr8be$[e-mail]> <4ft2uv$[e-mail]>
NNTP-Posting-Host: aplo139.spd.dsccc.com

In article <4ft2uv$[e-mail]>, Robert Fry <[e-mail]> wrote:
)[e-mail] (The Crow) writes:
)
)>Here is what I am trying to do, I want to find the last NON-ZERO digit of a
)>given factorial.  For instance,
)
)>5! = 120
)
)>so the last non-zero digit is 2.  I want to be able to do this up to 1000.
)>Problem is, no matter how huge of a data-type you use, there isn't any way for
)>the computer to handle 1000!, it is however possible to find the last non-zero
)>digit somehow.  One thing I have tried is as I went through mulitplying the
)>series of numbers in the factorial (5 * 4 * 3 * 2) I would remove all the
)>trailing ZEROS, I got this to work up to 789, but it wont work with 1000 and i
)>am not really sure why.  If anyone has a clue how I can do this let me know.
)
)As you already know, the number of digits in a factorial number grows
)very quickly. I calculated and printed out 1000! several years ago, and
)it more than fills a page with digits. However, since all you want to do
)is keep track of the last non-zero digit, why don't you simply perform
)the multiplications and keep just the last digit? I.e. 3!=6,
)4!=4*3!=4*6=24 and then just store the 4.
)
)This way you could use plain ints or longs, and your interim result
)(before dropping down to the last nonzero digit) will never be greater
)than 9x for x!.

Nice try, but no cigar.

    4! = 24 ~ 4
    5! = 5x4! ~ 5x4 = 20 ~ 0

Now you no longer have the last NON ZERO digit.

Mike
----
char *p="char *p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}

I don't speak for DSC.         <- They make me say that.