0540.cpp

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