@Override
  public boolean equals(Object o) {
    if (o instanceof LongStack) {
      LongStack otherStack = (LongStack)o;
      if (size != otherStack.size) return false;
      for (int i = 0; i < otherStack.size; i++) {
        if (data[i] != otherStack.data[i]) return false;
      }
      return true;
    }

    return false;
  }
@Override
  public boolean equals(Object o)