If this going to be more that once, you are better off creating 4001th hash in the array containing only the unique ones. Everytime you add and element chekc this array add to it too and vola! ur task will be greately reduced.

Just a thought! I really don't know of if you can get uniques without looping less. But per experience, hashes are fast and will not take that much time. Time it with 1000 first.