Faster algorithm to find unique element between two arrays?

Question

EDIT: For anyone new to this question, I have posted an answer clarifying what was going on. The accepted answer is the one I feel best answers my question

Answer 1

You can store the count of each value in a collection such as an array or hash map. O(n) then you can check the values of the other collection and stop as soon as you know you have a miss match. This could mean you only search half the second array on average.