面试题 9：用两个栈实现队列

09_QueueWithTwoStacks.cpp

template<typename T> void CQueue<T>::appendTail(const T& element) {
    stack1.push(element);
}

template<typename T> T CQueue<T>::deleteHead() {
    if(stack2.size() <= 0) {
        while(stack1.size() > 0) {
            T& data = stack1.top();
            stack1.pop();
            stack2.push(data);
        }
    }
    if(stack2.size() == 0) {
        throw new exception("queue is empty");
    }
    T head = stack2.top();
    stack2.pop();
    return head;
}