#include <cstddef>
#include <iostream>

class Vector {
private:
    int * buffer_;
    size_t size_;
    size_t capacity_;
public:
    Vector() {
        size_ = 0;
        capacity_ = 0;
        buffer_ = nullptr;
    }
    Vector(const Vector& other) {
        buffer_ = other.buffer_;
        size_ = other.size_;
        capacity_ = other.capacity_;
    }

    void reserve(size_t size) {
        int * new_buf = new int[size];
        for (size_t i = 0; i < capacity_; ++i) {
            new_buf[i] = buffer_[i];
        }
        capacity_ = size;
        delete [] buffer_;
        buffer_ = new_buf;
    }


    void push_back(int val) {
        if (size_ >= capacity_) {
            size_t new_cap = capacity_ ? capacity_ * 2 : 1;
            reserve(new_cap);
        }
        buffer_[size_++] = val;
    }
    void pop_back() {
        if (!size_)
            return;
        --size_;
    }

    const int operator[](size_t i) const {
        return buffer_[i];
    }

    int &operator[](size_t i) {
        return buffer_[i];
    }

    Vector& operator=(const Vector& other) {
        delete [] buffer_;
        buffer_ = other.buffer_;
        size_ = other.size_;
        return *this;
    }

    size_t size() {
        return size_;
    }

    ~Vector() {
        delete [] buffer_;
    }
};


int main() {
    Vector a;
    a.push_back(4);
    a.push_back(6);
    a.push_back(7);
    a.push_back(8);
    a.push_back(9);
    std::cout << "size " << a.size() << std::endl;
    for (size_t i = 0; i < a.size(); ++i) {
        std::cout << a[i] << ' ';
    }
    std::cout << std::endl;
    Vector b = a;

    std::cout << "size of b " << b.size() << std::endl;
    for (size_t i = 0; i < b.size(); ++i) {
        std::cout << b[i] << ' ';
    }
    std::cout << std::endl;

    a.pop_back();

    std::cout << "size " << a.size() << std::endl;
    for (size_t i = 0; i < a.size(); ++i) {
        std::cout << a[i] << ' ';
    }
    std::cout << std::endl;

    a.pop_back();

    std::cout << "size " << a.size() << std::endl;
    for (size_t i = 0; i < a.size(); ++i) {
        std::cout << a[i] << ' ';
    }
    std::cout << std::endl;

    a.pop_back();

    std::cout << "size " << a.size() << std::endl;
    for (size_t i = 0; i < a.size(); ++i) {
        std::cout << a[i] << ' ';
    }
    std::cout << std::endl;

    a.pop_back();

    std::cout << "size " << a.size() << std::endl;
    for (size_t i = 0; i < a.size(); ++i) {
        std::cout << a[i] << ' ';
    }
    std::cout << std::endl;

    a.pop_back();

    std::cout << "size " << a.size() << std::endl;
    for (size_t i = 0; i < a.size(); ++i) {
        std::cout << a[i] << ' ';
    }
    std::cout << std::endl;


}