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All leaked interview problems are collected from Internet.

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.

**Example 1:**

Input:[1,1,2,3,3,4,4,8,8]Output:2

**Example 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.

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