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Re: Sort one sequence by O(n) in time and O(1) in space

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On 10 February 2014 15:52, Chris Angelico <rosuav@gmail.com> wrote:
> On Tue, Feb 11, 2014 at 2:45 AM, Oscar Benjamin
> <oscar.j.benjamin@gmail.com> wrote:
>> Something like
>>
>>     mylist[:] = reorder_generator(mylist)
>>
>> won't work because the generator would need to access the data
>> non-sequentially (it would need to read elements after they were
>> overwritten).
>
> This would have O(1) space and O(n) time. It's absolutely perfect...
> except that you now don't technically have a list any more:
>
> mylist = reorder_generator(mylist)
>
> You can iterate over it, but can't index it. But hey, it complies with
> the space/time requirements!

That is very likely a practical solution for many problems involving
transposition. Doing this in Python is pretty artificial since a new
list object will likely use a lot less memory than the elements it
contains.

The practical use for such algorithms is in something like C and even
then it's often better to simply iterate in a different order. The
advantage of physically transposing the data is to improve memory
locality but this only makes sense if your transpose algorithm itself
has a good memory access pattern (which is likely impossible with O(1)
storage).


Oscar

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Sort one sequence by O(n) in time and O(1) in space Wesley <nispray@gmail.com> - 2014-02-09 04:13 -0800
  Re: Sort one sequence by O(n) in time and O(1) in space Asaf Las <roegltd@gmail.com> - 2014-02-09 04:29 -0800
  Re: Sort one sequence by O(n) in time and O(1) in space Chris Angelico <rosuav@gmail.com> - 2014-02-09 23:39 +1100
    Re: Sort one sequence by O(n) in time and O(1) in space Wesley <nispray@gmail.com> - 2014-02-09 18:09 -0800
      Re: Sort one sequence by O(n) in time and O(1) in space Dave Angel <davea@davea.name> - 2014-02-09 22:00 -0500
  Re: Sort one sequence by O(n) in time and O(1) in space Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-09 13:41 +0000
  Re: Sort one sequence by O(n) in time and O(1) in space Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-09 14:30 +0000
  Re: Sort one sequence by O(n) in time and O(1) in space Ni Wesley <nispray@gmail.com> - 2014-02-09 22:40 +0800
  Re: Sort one sequence by O(n) in time and O(1) in space Roy Smith <roy@panix.com> - 2014-02-09 10:05 -0500
    Re: Sort one sequence by O(n) in time and O(1) in space Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-09 23:14 +0000
      Re: Sort one sequence by O(n) in time and O(1) in space Roy Smith <roy@panix.com> - 2014-02-09 19:15 -0500
      Re: Sort one sequence by O(n) in time and O(1) in space Wesley <nispray@gmail.com> - 2014-02-09 18:26 -0800
        Re: Sort one sequence by O(n) in time and O(1) in space Sturla Molden <sturla.molden@gmail.com> - 2014-02-10 10:20 +0000
          Re: Sort one sequence by O(n) in time and O(1) in space Steven D'Aprano <steve@pearwood.info> - 2014-02-11 05:20 +0000
            Re: Sort one sequence by O(n) in time and O(1) in space Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-12 11:56 +1300
          Re: Sort one sequence by O(n) in time and O(1) in space Tim Daneliuk <tundra@tundraware.com> - 2014-02-10 23:37 -0600
          Re: Sort one sequence by O(n) in time and O(1) in space Tim Daneliuk <tundra@tundraware.com> - 2014-02-10 23:37 -0600
        Re: Sort one sequence by O(n) in time and O(1) in space Chris Angelico <rosuav@gmail.com> - 2014-02-10 21:37 +1100
        Re: Sort one sequence by O(n) in time and O(1) in space Sturla Molden <sturla.molden@gmail.com> - 2014-02-10 15:03 +0000
        Re: Sort one sequence by O(n) in time and O(1) in space Chris Angelico <rosuav@gmail.com> - 2014-02-11 02:23 +1100
        Re: Sort one sequence by O(n) in time and O(1) in space Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-10 15:45 +0000
        Re: Sort one sequence by O(n) in time and O(1) in space Chris Angelico <rosuav@gmail.com> - 2014-02-11 02:52 +1100
          Re: Sort one sequence by O(n) in time and O(1) in space Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-11 13:19 +1300
        Re: Sort one sequence by O(n) in time and O(1) in space Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-10 16:41 +0000
  Re: Sort one sequence by O(n) in time and O(1) in space Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-09 15:48 +0000
    Re: Sort one sequence by O(n) in time and O(1) in space Wesley <nispray@gmail.com> - 2014-02-09 18:07 -0800
  Re: Sort one sequence by O(n) in time and O(1) in space Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-09 21:31 +0000

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