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template<class E>
class AStack {
    ArrayList<E> *list { nullptr };
    
public:
    AStack() {
        list = new ArrayList<E>();
    }
    
    ~AStack() {
        if (list != nullptr) {
            delete list;
            list = nullptr;
        }
    }
    
    E top() {
        if (list->m_size > 0) {
            return list->get(list->m_size - 1);
        }
        return NULL;
    }
    
    void push(const E &element) {
        list->add(element);
    }
    
    E pop() {
        return list->removeAt(list->m_size - 1);
    }
    
    bool isEmpty() {
        return list->isEmpty();
    }
    
    void clear() {
        list->clear();
    }
 
};