Find duplicate element in array in time O(n)

Question

I have been asked this question in a job interview and I have been wondering about the right answer.

You have an array of numbers from 0 to n-1, one o

Answer 1

I suggest using a BitSet. We know N is small enough for array indexing, so the BitSet will be of reasonable size.

For each element of the array, check the bit corresponding to its value. If it is already set, that is the duplicate. If not, set the bit.