[Haskell-cafe] How to improve its performance ?
ajs at 2piix.com
Wed Mar 17 21:24:45 EDT 2010
On Mar 17, 2010, at 6:14 PM, Daniel Fischer wrote:
> I found it surprisingly not-slow (code compiled with -O2, as usual).
> There are two points where you waste time.
I found one big point where time is wasted: in computing the powerset
of a list. He's making 2^n elements, and then iterating through them
all and filtering, but only needs n^2 or n `choose` 2 of the
(depending on the semantics for his "groups").
The answer is to do something like:
allPairs list = [(x,y) | x <- list, y <- list]
to get it done in n^2 time.
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