Find the only unique element in an array of a million elements

Question

I was asked this question in a recent interview.

You are given an array that has a million elements. All the elements are duplicates except one. My task is to find t

Answer 1

Assuming the array is un-ordered, you can't. Every value is mutually exclusive to the next so nothing can be deduced about a value from any of the other values?

If it's an ordered array of values, then that's another matter and depends entirely on the ordering used.

I agree the easiest way is to have another container and store the frequency of the values.