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MathGroup Archive 2011

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Re: count zeros in a number

  • To: mathgroup at smc.vnet.net
  • Subject: [mg121820] Re: count zeros in a number
  • From: Richard Fateman <fateman at cs.berkeley.edu>
  • Date: Tue, 4 Oct 2011 01:30:21 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201110020636.CAA28027@smc.vnet.net> <j6brvm$8om$1@smc.vnet.net>

How disappointing that the usual crew did not come up with a way of 
solving this simply, arithmetically, like this:

(n = 0; While[GCD[24^24*55^55, 10^n] == 10^n, n++]; n - 1)

or

(n = 0; x = 24^24*55^55;
  While[Mod[x, 10] == 0, (x = x/10; n++)  ]; n)

or any of the numerous minor variants....

but instead resorted to conversion to strings or factoring.

The arithmentic methods may be slower since they rely on the slow 
implementation of looping constructs in Mathematica, but they
don't require any of the more esoteric features like
Exponents, Split, IntegerDigits, ...

RJF



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