I think you are repeating my steps :-) On sorted data (like [1..n])
quicksort is O(n^2).
Please read this thread:
http://www.nabble.com/(flawed-)-benchmark-:-sort-td15817832.html
All best
Christopher Skrzętnicki
2008/12/29 Adrian Neumann
Ah that's interesting. Now my Mergesort is exactly as fast as List.sort. I thought GHC was smart enough to do that kind of inter-module optimisation.
Still, Quicksort is twice as fast, so at least one argument for a Data.List.Sort package on hackage remains.
Am 29.12.2008 um 16:43 schrieb Bayley, Alistair:
From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Adrian Neumann
I don't consider myself to be a very advanced Haskell programmer, but I could come up with a Mergesort that beats List.sort, time- and spacewise.
On my machine List.sort takes ~10 sec, mergeSort 7, qs 4 (compiled with -O2). List.sort eats too much ram to sort 20.000.000 ints, my algorithms don't. QuickCheck says my implementations are correct.
Your single module might be benefiting from optimisation; specifically, specialisation to Ints, which would allow the dictionary lookup to be removed. Can you get the same performance if you move your mergeSort & qs functions into a separate module, and only export mergeSort & qs?
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