If you know that each array itself doesn't contain duplicate elements, you could try something along these lines: 
my (@a, @b);
# initialize @a and @b here

my %hash:
@hash{@a} = (1) x @a;

my @union        = @a, grep { !$hash{$_} } @b;
my @intersection =     grep {  $hash{$_} } @b;

[download]

That has the advantage of using only one hash, which might buy you some performance. But I don't know if it is actually faster than anything else.

(If you provide a small Benchmark with lists of typical sizes you might get much better answers; for example for a large number of small integers it might be more memory efficient to use vec than a hash, which might in turn result in some performance benefit.)

In reply to Re: Fast, Efficient Union and Intersection on arrays by moritz
in thread Fast, Efficient Union and Intersection on arrays by barvin

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