[leetcode-540-Single Element in a Sorted Array]

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.

思路：

二分查找。

class Solution {
public:
    int singleNonDuplicate(vector<int>& nums)
    {
        int n = nums.size(), left = 0, right = n - 1;
        while (left < right)
        {
            int mid = left + (right - left) / 2;
            if (mid % 2 == 0)
            {
                if (nums[mid] == nums[mid - 1])right = mid - 2;
                else if (nums[mid] == nums[mid + 1])left = mid + 2;
                else return nums[mid];
            }
            else
            {
                if (nums[mid] == nums[mid - 1])left = mid + 1;
                else if (nums[mid] == nums[mid + 1])right = mid - 1;
            }
        }
        return nums[left];
    }      
};