NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part1/7820

Internet Message Format | 1996-08-05 | 1.5 KB

Path: rs6.iaee.tuwien.ac.at!sor
From: [e-mail] (Evgeni Sorokin)
Newsgroups: comp.lang.pascal.misc,comp.lang.c++,comp.lang.c,comp.lang.pascal.borland
Subject: Re: Tough FACTORIAL math problem...
Followup-To: comp.lang.pascal.misc,comp.lang.c++,comp.lang.c,comp.lang.pascal.borland
Date: 19 Feb 1996 13:24:14 GMT
Organization: Vienna University of Technology, Austria
Message-ID: <4g9tlu$[e-mail]>
References: <4fr8be$[e-mail]>
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X-Newsreader: TIN [version 1.2 PL2]


One may use the following observations: all zeros come from 5's and 2's, and
there are more 2's than 5's.

Now, since last digit of product depend solely upon the last digits
of the  multipliers, we keep only the last digits. We also collect
all 2's separately, ahhihilating them with 5's, when possible.


var LastDigit, Count,
    Multiplier, Twos : integer;

const Stop = 1000;

begin
  LastDigit:=1;
  Twos:=0;
  for Count:=1 to Stop do begin
    While (Multiplier mod 2) = 0 do begin
      Twos:=Twos+1;
      Multiplier:=Multiplier div 2;
    end;
    While (Multiplier mod 5) = 0 do begin
      Twos:=Twos-1;
      Multiplier:=Multiplier div 5;
    end;
    LastDigit:=(LastDigit*Multiplier) mod 10;
  end;
  for Count:=1 to Twos do
    LastDigit:=(LastDigit*2) mod 10;
end.





--
Zhenya Sorokin

E-mail     : [e-mail], [e-mail]
Paper-mail : E. Sorokin, Gusshausstr. 27/359-4, 1040 Vienna, Austria
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