Hi mave,

The text-book way of doing qsort 'properly' (already I'm on flame-war ground :) ), is use the median-three variant (median-three vairant means pick the first, middle and last item and choose the median of these for the partition point)with three speed enhancements: first use the two remaining items from the median-three step as sentinels (instead of having a second conditional in the innerloop), next at n=20-60ish (hardware dependent constant) switch to insertion sort, and lastly when deciding wether to swap or keep in place an equal item, choose to swap it.

Of course, all this is meaningless babble. The best thing to do is go in and test it. Hmm, unfortunately my boss got back from out of town work and is on the rampage this morning handing out more work for us all :) . I suggest a randomness test on output (chi-squared) and/or running sample data and counting the number of swaps. I also suggest using this when testing:
my @list = map $_->[1], sort {$a->[0]<=>$b->[0]} map [rand,$_], (0..99);

Which should be much faster on larger sets, and you can change the rand part to int rand $n, which can have $n be the (inverse of the) chance that two items will be equal.

Good Luck,
Gryn

In reply to Re: Re: Re: random permutations by gryng
in thread random permutations by mave

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