Perl Style: Embrace Hashes

Until you start thinking in terms of hashes, you're not thinking in Perl. They can often replace lengthy loops or complex algorithms.
Use a hash whenever you want to represent a set, a relation, a table, a structure, or a record.
The words `in', `unique', `first', and `duplicate' should all set off Pavlovian screams of `HASH!' If you find them in the same sentence as `array', you're probably doing something wrong.