Factors of an integer: Difference between revisions
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=={{Header|Haskell}}==
Using D. Amos module Primes [https://web.archive.org/web/20121130222921/http://www.polyomino.f2s.com/david/haskell/codeindex.html] for finding prime factors
<lang Haskell>import HFM.Primes(primePowerFactors)
import Data.List
-- primePowerFactors :: Integer -> [(Integer,Int)]
factors = map product.
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<lang Haskell>factors_naive n = [i | i <-[1..n], (mod n i) == 0]</lang>
<lang Haskell>factors_naive 6
[1,2,3,6]</lang>
Factor, cofactor. Rearrange a list of tuples to a sorted list
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[i | i <-
[1..truncate (sqrt (fromIntegral n))]
, (mod n i) == 0]] ))</lang>
<lang Haskell>factors_co 6
[1,2,3,6]</lang>
A cleaner, simplified version of the code above, without the sorting nor the tuples, increasing speed and making it possible to see results in real time (if using GHCi)
<lang Haskell>import Data.List
factors n = lows ++ (reverse $ map (div n) lows)
where lows = filter ((== 0) . mod n) [1..truncate . sqrt $ fromIntegral n]</lang>
<lang Haskell>*Main> :set +s
*Main> factors 120
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