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Re: Is my implementation of happy number OK

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From Ian Kelly <ian.g.kelly@gmail.com>
Date Fri, 1 May 2015 09:03:32 -0600
Subject Re: Is my implementation of happy number OK
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On Fri, May 1, 2015 at 2:27 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> Rather than 10**7, how about trying (10**500 + 2). Is it happy?
>
> Using the Python code from Wikipedia:
> https://en.wikipedia.org/wiki/Happy_number
>
> SQUARE = dict([(c, int(c)**2) for c in "0123456789"])
> def is_happy(n):
>   while (n > 1) and (n != 4):
>     n = sum(SQUARE[d] for d in str(n))
>   return n == 1
>
>
> I can calculate whether n=10**500 + 2 is happy in less than a millisecond on
> my computer.

Not really the most exciting example, since the following number in
the sequence would be 5. But a random sequence of 500 non-zero digits
doesn't seem to take substantially longer.

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Thread

Is my implementation of happy number OK Cecil Westerhof <Cecil@decebal.nl> - 2015-04-30 17:59 +0200
  Re: Is my implementation of happy number OK Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-04-30 17:04 +0000
  Re: Is my implementation of happy number OK Ian Kelly <ian.g.kelly@gmail.com> - 2015-04-30 11:37 -0600
    Re: Is my implementation of happy number OK Cecil Westerhof <Cecil@decebal.nl> - 2015-04-30 21:05 +0200
  Re: Is my implementation of happy number OK Dave Angel <davea@davea.name> - 2015-04-30 14:53 -0400
    Re: Is my implementation of happy number OK Cecil Westerhof <Cecil@decebal.nl> - 2015-04-30 22:35 +0200
      Re: Is my implementation of happy number OK Dave Angel <davea@davea.name> - 2015-04-30 17:31 -0400
    Re: Is my implementation of happy number OK Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-04-30 23:31 +0000
      Re: Is my implementation of happy number OK Dave Angel <davea@davea.name> - 2015-04-30 19:52 -0400
        Re: Is my implementation of happy number OK Cecil Westerhof <Cecil@decebal.nl> - 2015-05-01 06:36 +0200
        Re: Is my implementation of happy number OK Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-05-01 07:23 +0000
          Re: Is my implementation of happy number OK Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-01 18:27 +1000
            Re: Is my implementation of happy number OK Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-01 09:03 -0600
            Re: Is my implementation of happy number OK Peter Otten <__peter__@web.de> - 2015-05-01 20:13 +0200
              Re: Is my implementation of happy number OK Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2015-05-02 21:23 +0000

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