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

How about using a BloomFilter impl: like http://code.google.com/p/java-bloomfilter/ first do a bloom.contains(element) if true continue if false bloom.add(element).

At the end count the number of elements added. Bloomfilter needs approx. 250mb memory to store 100000000 elements at 10bits per element.

Problem is that false positives are possible in BloomFilters and can only be minimized by increasing the number of bits per element. This could be addressed by two BloomFilters with different hashing that need to agree.