540. Single Element in a Sorted Array Difficulty：Medium

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.

算法分析：已知要用O(log n)的时间复杂度的算法，那么这里选择用二分法。用left, mid, right表示左中右三点的下标，要有孤立值，数组长度是奇数，那么情况有三种：孤立值在左边，孤立值在中间，孤立值在右边。当孤立值在左边的时候，mid为偶数；当孤立值在右边的时候mid为奇数，分别对应前面的两个例子，具体见代码。Python和C类似，在此只列出C。

int singleNonDuplicate(int* nums, int numsSize) {
int left = 0, right = numsSize - 1, mid, i;
while(left < right)
{
mid = (left + right) / 2;
if(mid % 2 == 1)
mid--;
if(nums[mid] != nums[mid + 1]) //孤立值在左边
right = mid;
else //孤立值在右边
left = mid + 2;
}
return nums[left];
}