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:

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

Example 2:

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Input: [3,3,7,7,10,11,11]
Output: 10

Note: Your solution should run in O(log n) time and O(1) space.

很经典的题，用异或。

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class Solution {
public:
    int singleNonDuplicate(vector<int>& nums) {
        int ans = 0;
        for (auto i : nums) {
            ans ^= i;
        }
        return ans;
    }
};