The description is still incomplete and the task is still not novel at all. Please, don't resolve issues for no reason.

• Non-standard header files should not be used
• Initial solution shouldn't include using namespace std, and the tests shouldn't rely on the user's solution to include it
• The input type should be std::vector<unsigned> and the output type should be unsigned
• Nothing's said about duplicate numbers and how they should be handled, e.g. what range is {1, 2, 2, 2, 1, 1} supposed to represent?
• No random tests

I'm pretty sure this is a duplicate as well.