# 99 questions/Solutions/36

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using <tt>primeFactors</tt> from problem 35 to generate the list of prime factors in ascending order, and <tt>encode</tt> from problem 10 to compress this list to a list of numbers paired with their multiplicity. | using <tt>primeFactors</tt> from problem 35 to generate the list of prime factors in ascending order, and <tt>encode</tt> from problem 10 to compress this list to a list of numbers paired with their multiplicity. | ||

+ | |||

+ | |||

+ | Without relying on <tt>encode</tt> from problem 10, but using <tt>group</tt> from <tt>Data.List</tt>: | ||

+ | |||

+ | <haskell> | ||

+ | prime_factors_mult = map encode . group . primeFactors | ||

+ | where encode xs = (head xs, length xs) | ||

+ | </haskell> |

## Revision as of 08:02, 19 August 2012

(**) Determine the prime factors of a given positive integer.

Construct a list containing the prime factors and their multiplicity.

prime_factors_mult n = map swap $ encode $ primeFactors n where swap (x,y) = (y,x)

using `primeFactors` from problem 35 to generate the list of prime factors in ascending order, and `encode` from problem 10 to compress this list to a list of numbers paired with their multiplicity.

Without relying on `encode` from problem 10, but using `group` from `Data.List`:

prime_factors_mult = map encode . group . primeFactors where encode xs = (head xs, length xs)