in reply to To Hash or to Array--Uniqueness is the question.

Never invent the wheel again: use the List::MoreUtils module which has a uniq-function.
uniq LIST

Returns a new list by stripping duplicate values in LIST. The order of elements in the returned list is the same as in LIST. In scalar context, returns the number of unique elements in LIST. 

my @x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 1 2 3 5 4
    my $x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 5

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CountZero

"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law

In Section Seekers of Perl Wisdom