Step 3 of 6
std::set
std::set<T> holds unique values, sorted. Inserting a duplicate does nothing.
std::set<int> s = {5, 1, 5, 3}; // {1, 3, 5}
s.insert(2);
s.contains(3); // true (C++20)
s.count(9); // 0
Your turn: write std::vector<std::string> unique_sorted(const std::vector<std::string>& v) that returns the distinct strings in sorted order.