Use a hash. Here's code to do both and more. It assumes that each elem
+ent is unique in a given array:

    @union = @intersection = @difference = ();
    %count = ();
    foreach $element (@array1, @array2) { $count{$element}++ }
    foreach $element (keys %count) {
        push @union, $element;
        push @{ $count{$element} > 1 ? \@intersection : \@difference }
+, $element;
    }
Note that this is the symmetric difference, that is, all elements in e
+ither A or in B but not in both. Think of it as an xor operation.
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$_=$,=q,\,@4O,,s,^$,$\,,s,s,^,b9,s,
$_^=q,$\^-]!,,print
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