This works whether the arrays contain duplicate elements or not:

my %a = map { $_ => 1 } @a;
my %b = map { $_ => 1 } @b;

@c = grep { !$b{$_} } @a;
@d = grep { !$a{$_} } @b;

[download]

In reply to Re^2: Algorithm for cancelling common factors between two lists of multiplicands by ikegami
in thread Algorithm for cancelling common factors between two lists of multiplicands by BrowserUk

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