[Haskell-cafe] newbie optimization question
plragde at uwaterloo.ca
Sun Oct 28 09:13:31 EDT 2007
For the purposes of learning, I am trying to optimize some variation of
the following code for computing all perfect numbers less than 10000.
divisors i = [j | j<-[1..i-1], i `mod` j == 0]
main = print [i | i<-[1..10000], i == sum (divisors i)]
I know this is mathematically stupid, but the point is to do a moderate
nested-loops computation. On my 2.33GHz dual-core MacBookPro, the
obvious C program takes about .3 seconds, and a compiled OCaML program
(tail recursion, no lists) about .33 seconds. The above takes about 4
I've tried using foldl', and doing explicit tail recursion with strict
accumulators, but I can't get the running time below 3 seconds. Is it
possible to come within striking distance of the other languages?
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