au

vector init_vector() {
  vector v;
  v.size = 0;
  v.mem_size = 1;
  v.a = malloc(sizeof (int));
  return v;
}

void push_back(vector v, int x) {
  if (v.size + 1 >= v.mem_size) {
    v.mem_size *= 2;
    v.a = realloc(v.a, sizeof(int) * (unsigned)v.mem_size);
  }
  v.a[v.size] = x;
  v.size += 1;
}