$i{$_}++ for (@a);
$i{$_}-- for (@b);

@c=grep { $i{$_} > 0 } keys @a;
@d=grep { $i{$_} < 0 } keys @b;

[download]
btw, are your sample solution arrays right?

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

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