Given a sorted array consisting of only integers where every element appears twice except for one element which appears once. Find this single element that appears only once.
Input: [1,1,2,3,3,4,4,8,8] Output: 2
Input: [3,3,7,7,10,11,11] Output: 10
Note: Your solution should run in O(log n) time and O(1) space.