In less-than-linear time, find the duplicate in a sorted array

Question

Today, an interviewer asked me this question. My immediate response was that we could simply do a linear search, comparing the current element with the previous element in t

Answer 1

How about that? (recursion style)

public static int DuplicateBinaryFind(int[] arr, int left, int right)
{
   int dup =0;

   if(left==right)
   {
      dup = left;
   }
   else
   {
        int middle = (left+right)\2;
        if(arr[middle]