9.cpp

class CQueue
{
  private:
    stack<int> main_stk, assist_stk;

  public:
    CQueue()
    {
        return;
    }

    void appendTail(int value)
    {
        main_stk.push(value);
    }

    int deleteHead()
    {
        if (main_stk.empty())
            return -1;
        while (!main_stk.empty())
        {
            assist_stk.push(main_stk.top());
            main_stk.pop();
        };
        int ans = assist_stk.top();
        assist_stk.pop();
        while (!assist_stk.empty())
        {
            main_stk.push(assist_stk.top());
            assist_stk.pop();
        };
        return ans;
    }
};

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue* obj = new CQueue();
 * obj->appendTail(value);
 * int param_2 = obj->deleteHead();
 */