Counting unique element in large array

Question

One of my colleagues was asked this question in an interview.

Given a huge array which stores unsigned int. Length of array is 100000000. Find the effective

Answer 1

Hashing in this case is not inneficient. The cost will be approximately O(N) (O(N) for iterating over the array and ~O(N) for iterating over the hashtable). Since you need O(N) for checking each element, the complexity is good.