Find an element in an infinite length sorted array

Question

Given an infinite length sorted array having both positive and negative integers. Find an element in it.

EDIT
All the elements in the array are

Answer 1

Here is another implementation which use 2^n to search occurrence of element itself, and then gives this sub-array to binary search

e.g.
 arr = 1,2,3,4,5,6,7,8,9,-1,-1,-1,-1,-1,-1...........
 num = 8;

efficiency = 2logn