mirror of
https://github.com/correl/euler.git
synced 2024-11-27 19:19:50 +00:00
28 lines
735 B
Haskell
28 lines
735 B
Haskell
|
{-
|
||
|
|
Find the largest prime factor of a composite number.
|
||
|
|
|
||
|
|
The prime factors of 13195 are 5, 7, 13 and 29.
|
||
|
|
What is the largest prime factor of the number 600851475143 ?
|
||
|
|
-}
|
||
|
|
|
||
|
|
import Text.Printf
|
||
|
|
|
||
|
|
pfactor :: (Integral a) => a -> [a]
|
||
|
|
pfactor n = pfactor_ n []
|
||
|
|
|
||
|
|
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_next :: (Integral a) => a -> a -> a
|
||
|
|
pfactor_next n factor
|
||
|
|
| n == factor = factor
|
||
|
|
| n `rem` factor == 0 = factor
|
||
|
|
| otherwise = pfactor_next n (factor + 1)
|
||
|
|
|
||
|
|
main = do
|
||
|
|
printf "Largest prime factor of 600851475143: %d\n" (last (pfactor 600851475143) :: Int)
|