Terry Reedy wrote:
On 8/26/2011 8:23 PM, Antoine Pitrou wrote:
I would only agree as long as it wasn't too much worse
than O(1). O(log n) might be all right, but O(n) would be
unacceptable, I think.
It also depends a lot on *actual* measured performance
Amen. Some regard O(n*n) sorts to be, by definition, 'worse' than
O(n*logn). I even read that in an otherwise good book by a university
professor. Fortunately for Python users, Tim Peters ignored that
'wisdom', coded the best O(n*n) sort he could, and then *measured* to
find out what was better for what types and lengths of arrays. So not we
have a list.sort that sometimes beats the pure O(nlog) quicksort of C
libraries.
A nice story, but Quicksort's worst case is O(n*n) too.
http://en.wikipedia.org/wiki/Quicksort
timsort is O(n) in the best case (all items already in order).
You are right though about Tim Peters doing extensive measurements:
http://bugs.python.org/file4451/timsort.txt
If you haven't read the whole thing, do so. I am in awe -- not just
because he came up with the algorithm, but because of the discipline Tim
demonstrated in such detailed testing. A far cry from a couple of timeit
runs on short-ish lists.
--
Steven
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