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Re: Python 3.3 vs. MSDOS Basic

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From Serhiy Storchaka <storchaka@gmail.com>
Subject Re: Python 3.3 vs. MSDOS Basic
Date Tue, 19 Feb 2013 22:28:25 +0200
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On 19.02.13 20:31, Ian Kelly wrote:
> On Tue, Feb 19, 2013 at 7:46 AM, Tim Daneliuk <tundra@tundraware.com> wrote:
>> Are you sure you wouldn't like to share with the class?  I'd be interested
>> in seeing your approach...
>
> Very well:
>
> def collatz(n, memo):
>      if n not in memo:
>          if n % 2 == 0:
>              next_n = n // 2
>          else:
>              next_n = 3 * n + 1
>          memo[n] = collatz(next_n, memo) + 1
>      return memo[n]
>
> def run_collatz(upper):
>      table = {1: 0}
>      max_n = max(range(1, upper), key=lambda n: collatz(n, table))
>      return max_n, table[max_n]
>
>>>> run_collatz(1000000)
> (837799, 524)
>
> It could certainly be optimized further, but at about 4 seconds it's
> already fast enough for most purposes.

10-15% faster:

def f(M):
     def g(n, cache = {1: 0}):
         if n in cache:
             return cache[n]
         if n % 2:
             m = 3 * n + 1
         else:
             m = n // 2
         cache[n] = count = g(m) + 1
         return count
     num = max(range(2, M + 1), key=g)
     return num, g(num)

print(*f(1000000))

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Thread

Python 3.3 vs. MSDOS Basic John Immarino <johimm@gmail.com> - 2013-02-18 11:13 -0800
  Re: Python 3.3 vs. MSDOS Basic Chris Angelico <rosuav@gmail.com> - 2013-02-19 08:55 +1100
  Re: Python 3.3 vs. MSDOS Basic Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-18 14:54 -0700
    Re: Python 3.3 vs. MSDOS Basic Tim Daneliuk <tundra@tundraware.com> - 2013-02-19 08:46 -0600
      Re: Python 3.3 vs. MSDOS Basic Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-19 11:31 -0700
        Re: Python 3.3 vs. MSDOS Basic Tim Daneliuk <tundra@tundraware.com> - 2013-02-20 08:21 -0600
          Re: Python 3.3 vs. MSDOS Basic Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-20 11:38 -0700
            Re: Python 3.3 vs. MSDOS Basic Tim Daneliuk <tundra@tundraware.com> - 2013-02-20 16:49 -0600
              Re: Python 3.3 vs. MSDOS Basic Tim Daneliuk <tundra@tundraware.com> - 2013-02-20 16:59 -0600
      Re: Python 3.3 vs. MSDOS Basic Serhiy Storchaka <storchaka@gmail.com> - 2013-02-19 22:28 +0200
      Re: Python 3.3 vs. MSDOS Basic Chris Angelico <rosuav@gmail.com> - 2013-02-20 08:39 +1100
        Re: Python 3.3 vs. MSDOS Basic Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-02-20 18:32 +1300
  Re: Python 3.3 vs. MSDOS Basic Chris Angelico <rosuav@gmail.com> - 2013-02-19 08:56 +1100
  Re: Python 3.3 vs. MSDOS Basic Chris Angelico <rosuav@gmail.com> - 2013-02-19 08:58 +1100
    Re: Python 3.3 vs. MSDOS Basic John Immarino <johimm@gmail.com> - 2013-02-18 17:39 -0800
      Re: Python 3.3 vs. MSDOS Basic Chris Angelico <rosuav@gmail.com> - 2013-02-19 14:01 +1100
        Re: Python 3.3 vs. MSDOS Basic Nick Mellor <thebalancepro@gmail.com> - 2013-02-18 20:17 -0800
        Re: Python 3.3 vs. MSDOS Basic Nick Mellor <thebalancepro@gmail.com> - 2013-02-18 20:17 -0800
    Re: Python 3.3 vs. MSDOS Basic John Immarino <johimm@gmail.com> - 2013-02-18 17:39 -0800
      Re: Python 3.3 vs. MSDOS Basic Neil Cerutti <neilc@norwich.edu> - 2013-02-20 17:06 +0000
  Re: Python 3.3 vs. MSDOS Basic Chris Angelico <rosuav@gmail.com> - 2013-02-19 09:01 +1100
  Re: Python 3.3 vs. MSDOS Basic Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-18 15:15 -0700
  Re: Python 3.3 vs. MSDOS Basic Alexander Blinne <news@blinne.net> - 2013-02-19 01:11 +0100
  Re: Python 3.3 vs. MSDOS Basic Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-02-18 19:36 -0500
    Re: Python 3.3 vs. MSDOS Basic John Immarino <johimm@gmail.com> - 2013-02-18 17:47 -0800
    Re: Python 3.3 vs. MSDOS Basic John Immarino <johimm@gmail.com> - 2013-02-18 17:47 -0800
  Re: Python 3.3 vs. MSDOS Basic Terry Reedy <tjreedy@udel.edu> - 2013-02-18 19:50 -0500
    Re: Python 3.3 vs. MSDOS Basic Piet van Oostrum <piet@vanoostrum.org> - 2013-02-19 12:42 +0100
      Re: Python 3.3 vs. MSDOS Basic Alexander Blinne <news@blinne.net> - 2013-02-20 01:23 +0100
        Re: Python 3.3 vs. MSDOS Basic Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-19 18:04 -0700
  Re: Python 3.3 vs. MSDOS Basic Terry Reedy <tjreedy@udel.edu> - 2013-02-19 00:28 -0500
  Re: Python 3.3 vs. MSDOS Basic Anssi Saari <as@sci.fi> - 2013-02-19 12:52 +0200
  Re: Python 3.3 vs. MSDOS Basic Serhiy Storchaka <storchaka@gmail.com> - 2013-02-19 13:13 +0200
  Re: Python 3.3 vs. MSDOS Basic Olive <diolu.remove_this_part@bigfoot.com> - 2013-02-19 15:02 +0100

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