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Fixed Haskell 003

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Correl Roush 2011-10-11 13:02:51 -04:00
parent 09031a099d
commit 2c0a857bd4
1 changed files with 11 additions and 12 deletions
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23
haskell/e003.hs
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@ -8,20 +8,19 @@ What is the largest prime factor of the number 600851475143 ?
import Text.Printf
pfactor :: (Integral a) => a -> [a]
pfactor n = pfactor_ n []
pfactor n = pfactor_ n [] 2
pfactor_ :: (Integral a) => a -> [a] -> [a]
pfactor_ n factors = do
let next = pfactor_next n 2
if next == n
then factors ++ [n]
else pfactor_ (n `div` next) (factors ++ [next])
pfactor_ n factors start =
let next = pfactor_next n start in
if n == next
then n:factors
else pfactor_ (n `div` next) (next:factors) next
pfactor_next :: (Integral a) => a -> a -> a
pfactor_next n factor
| n == factor = factor
| n `rem` factor == 0 = factor
| otherwise = pfactor_next n (factor + 1)
pfactor_next n last
| n <= last = n
| otherwise = head (filter (\x -> n `rem` x == 0 || n == x) [last..n])
main = do
printf "Largest prime factor of 600851475143: %d\n" (last (pfactor 600851475143) :: Int)
printf "Largest prime factor of 13195: %d\n" (head (pfactor 13195) :: Integer)
printf "Largest prime factor of 600851475143: %d\n" (head (pfactor 600851475143) :: Integer)