Puzzle : finding out repeated element in an Array

Question

Size of an array is n.All elements in the array are distinct in the range of [0 , n-1] except two elements.Find out repeated element without using extra temporary array with con

Answer 1

Pick two distinct random indexes. If the array values at those indexes are the same, return true.

This operates in constant time. As a bonus, you get the right answer with probability 2/n * 1/(n-1).