Vector

template<typename T>
class Vector {
  int _size = 0, _cap = 1;
  T *c = new T[1];

public:
  bool empty() const { return _size == 0; }
  int size() const { return _size; }
  T& operator[](int idx) { return c[idx]; }
  void pop_back() { if (_size > 0) --_size; }

  void push_back(T __x) {
    if (_size == _cap) {
      T *old_c = c;
      c = new T[2 * _cap];
      memcpy(c, old_c, _cap * sizeof(T));
      _cap *= 2;
      delete[] old_c;
    }
    c[_size++] = __x;
  }
};