题目：

题解：

int singleNonDuplicate(int* nums, int numsSize) {
    int low = 0, high = numsSize - 1;
    while (low < high) {
        int mid = (high - low) / 2 + low;
        mid -= mid & 1;
        if (nums[mid] == nums[mid + 1]) {
            low = mid + 2;
        } else {
            high = mid;
        }
    }
    return nums[low];
}