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Unless the individual values get very large, I think the easiest would be to factor them:

sub combine_factors { my $list = shift; my $factors = {}; for (@$list) { for (factors($_)) { ++$factors->{$_}; } } $factors; } my $fa = combine_factors(\@a); my $fb = combine_factors(\@b); ($fa->{$_} ||= 0) -= $fb->{$_} for keys %$fb; my @c = map +($_) x $fa->{$_}, grep $fa->{$_} > 0, keys %$fa; my @d = map +($_) x -$fa->{$_}, grep $fa->{$_} < 0, keys %$fa;

This has the disadvantage that it will leave a list of primes: @c == (3, 5, 11), @d == (2, 2, 2, 23). I'm not sure how you'd retain the original composites (or parts thereof), nor how you'd define which composites to keep, so I chose to ignore that aspect of it.

Hugo


In reply to Re: Algorithm for cancelling common factors between two lists of multiplicands by hv
in thread Algorithm for cancelling common factors between two lists of multiplicands by BrowserUk

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