Details about pythons set implementation

Diez B. Roggisch deets at nospam.web.de
Fri Jan 4 18:41:02 CET 2008


bukzor schrieb:
> On Jan 4, 9:08 am, Sion Arrowsmith <si... at chiark.greenend.org.uk>
> wrote:
>> Hrvoje Niksic  <hnik... at xemacs.org> wrote:
>>
>>> BTW if you're using C++, why not simply use std::set?
>> Because ... how to be polite about this? No, I can't. std::set is
>> crap. The implementation is a sorted sequence -- if you're lucky,
>> this is a heap or a C array, and you've got O(log n) performance.
>> But the real killer is that requirement for a std::set<T> is that
>> T::operator< exists. Which means, for instance, that you can't
>> have a set of complex numbers....
>>
>> --
>> \S -- si... at chiark.greenend.org.uk --http://www.chaos.org.uk/~sion/
>>    "Frankly I have no feelings towards penguins one way or the other"
>>         -- Arthur C. Clarke
>>    her nu becomeþ se bera eadward ofdun hlæddre heafdes bæce bump bump bump
> 
> Why cant you implement < for complex numbers? Maybe I'm being naive,
> but isn't this the normal definition?
>     a + bi < c + di iff sqrt(a**2 + b**2) < sqrt(c**2, d**2)
> 
> How do you implement a set without sorting?
> 
> Are you expecting better than O(log n)?

Of course, hashing does O(1) (most of the time, with a sane hash of course.)

Diez



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