Спринт 6. Амортизированная сложность.

#include <algorithm>
#include <deque>
#include <string>
#include <iostream>

using namespace std;

struct Ticket {
    int id;
    string name;
};

class TicketOffice {
public:
    void PushTicket(const string& name) {
        last_id_++;
        tickets_.push_back({last_id_, name});
    }

    int GetAvailable() const {
        return tickets_.size();
    }

    int GetAvailable(const string& name) const {
        return count_if(begin(tickets_), end(tickets_), [name](const Ticket& T){return name==T.name;});
    }

    void Invalidate(int minimum) {
        while (!tickets_.empty() && tickets_.front().id <= minimum){
            tickets_.pop_front();
        }
    }
private:
    int last_id_ = 0;
    deque<Ticket> tickets_;
};

int main(){
    TicketOffice tickets;

    tickets.PushTicket("Swan Lake");
    tickets.PushTicket("Swan Lake");
    tickets.PushTicket("Boris Godunov");
    tickets.PushTicket("Boris Godunov");
    tickets.PushTicket("Swan Lake");
    tickets.PushTicket("Boris Godunov");
    tickets.PushTicket("Boris Godunov");

    cout << tickets.GetAvailable() << endl;
    cout << tickets.GetAvailable("Swan Lake") << endl;
    cout << tickets.GetAvailable("Boris Godunov") << endl;

    tickets.Invalidate(3);

    cout << tickets.GetAvailable() << endl;
    cout << tickets.GetAvailable("Swan Lake") << endl;
    cout << tickets.GetAvailable("Boris Godunov") << endl;

    tickets.PushTicket("Swan Lake");
    tickets.PushTicket("Swan Lake");

    cout << tickets.GetAvailable("Swan Lake") << endl;
}