Solution: Observer Design Pattern

#include <iostream>
#include <list>
#include <string>
class Buyer {
 public:
  virtual ~Buyer(){};
  virtual void notify() = 0;
};
class Shop {
 public:
  void registerBuyer(Buyer* observer) {
    observers.push_back(observer);
  }
  void unregisterBuyer(Buyer* observer) {
    observers.remove(observer);
  }
  void notifyBuyers() {
    for (auto observer: observers) observer->notify();
  }
 private:
  std::list<Buyer *> observers;
};
class Directcustomer : public Buyer {
 public:
    Directcustomer(Shop& subject) : shop_obj(subject) {
        this->shop_obj.registerBuyer(this);
    }
    void notify() override {
        
        std::cout << "Dear customer, the product you requested is now back in stock \n";
        
    }
 private: 
    Shop& shop_obj;
};
class Partnercustomer : public Buyer {
 public:
    Partnercustomer(Shop& subject) : shop_obj(subject) {
        this->shop_obj.registerBuyer(this);
    }
    void notify() override {
   
        std::cout << "Dear partner, the product you requested is now back in stock \n";
        
    }
 private: 
    Shop& shop_obj;
};
int main() {
    Shop* subject = new Shop;
    Buyer* George = new Directcustomer(*subject);
    Buyer* Xyz_company = new Partnercustomer(*subject);
    subject->notifyBuyers();
    delete George;
    delete Xyz_company;
    delete subject;
}