Uhh ... you do realize that you just implemented a very rudimentary hash table in Perl using ... wait for it ... hashes! Except, you don't handle collisions. What's wrong with: 
sub intersection {
  my ( $list1, $list2 ) = @_;

  my %hash;
  @hash{@$list1} = undef;

  my @intersection = grep { exists $hash{$_} } @$list2;

  return @intersection
}

[download]

Update: Fixed mistake in my code (map -> grep) Compare mine to yours and I think you'll notice a difference.

My criteria for good software:
  1. Does it work?
  2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

In reply to Re: Finding an intersection of two sets, lean and mean by dragonchild
in thread Finding an intersection of two sets, lean and mean by Sinister

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