# P35 - Determine the prime factors of a given positive integer.

*Author: Philip Potter*

# Specification

P35 (**) Determine the prime factors of a given positive integer. Construct a flat list containing the prime factors in ascending order.

# Example

> say ~prime_factors 315 3 3 5 7

Source code: P35-rhebus.pl

use v6; sub prime_factors (Int $n) { my $residue = $n; my @values = (2,3,*+2 ... * > $n); gather for @values -> $k { while $residue %% $k { # try 'take 0+$k' to work around a known rakudo issue (2010-09-05) take $k; $residue /= $k; } last if $residue == 1; # This if block is an optimisation which reduces number of iterations # for numbers with large prime factors (such as large primes) # It can be removed without affecting correctness. if $k > sqrt $residue { take $residue; last; } } } say ~prime_factors($_) for 2..20; say ~prime_factors(315); say ~prime_factors(1723);