题6：用两个栈实现队列

using namespace std;

template <typename T>
class MyQueue
{
public:
MyQueue();
~MyQueue();
void appendTail(const T& node);
T deleteHead();
private:
stack<T> stack1;
stack<T> stack2;
};

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

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

return head;
}