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

Sorting is a good idea. However type of sorting depends on range of possible values. For small range counting sort would be good. While dealing with such a big array it would be efficient to use multiple cores - radix sort might be good.