用两个栈模拟一个队列

思路：
让栈A提供入队功能，栈B提供出队功能。
入队列：栈A。
出队列：如果栈B不为空，直接弹出栈B的栈顶数据；如果栈B为空，则依次弹出栈A的数据，放入栈B中，再弹出栈B的栈顶数据。

方法一：

#include<iostream>#include<stack>#include<string>using namespace std;template<class T>struct MyQueue{    void Enqueue(T t)    {        s1.push(t);    }    T Dequeue()    {        if(s2.empty())        {            if(0 == s1.size())            {                exit(1);            }            while(!s1.empty())            {                s2.push(s1.top());                s1.pop();            }        }        T retVal = s2.top();        s2.pop();        return retVal;    }    stack<T> s1;    stack<T> s2;};int main(){    MyQueue<int> mq;    int begin = 0;    int end = 10;    int i;    for(i = begin; i < end; i++)    {        mq.Enqueue(i);    }    for(i = begin; i < end; i++)    {        cout<<mq.Dequeue()<<' ';    }    cout<<endl;    MyQueue<float> mq2;    mq2.Enqueue(1.1f);    mq2.Enqueue(2.2f);    cout << mq2.Dequeue() << endl;    MyQueue<string> mq3;    string s1 = "hello";    string s2 = "world";    mq3.Enqueue(s1);    mq3.Enqueue(s2);    cout << mq3.Dequeue() << endl;    return 0;}

运行结果：

0 1 2 3 4 5 6 7 8 91.1helloPress any key to continue

方法二：

#include <iostream>using namespace std;struct Node{public:    Node(int i):data(i),next(NULL){}    int data;    Node *next;};class Stack{public:    Stack():top(NULL){}    void Push(Node node);   //入栈    int Pop();              //出栈    bool IsEmpty();         //是否为空    void Print();           //打印所有元素private:    Node *top;};void Stack::Push(Node node){    Node *n = new Node(node.data);    n->next = top;    top = n;}int Stack::Pop(){    if (IsEmpty())    {           cout << "Stack Empty!" << endl;        exit(1);    }    else    {        int topVal = top->data;        Node *temp = top;        top = top->next;        delete temp;        return topVal;    }}bool Stack::IsEmpty(){    if (NULL == top)    {        return 1;    }    else    {        return 0;    }}void Stack::Print(){    if(IsEmpty())    {        cout << "Inner Stack Empty!" << endl;    }    else    {        Node *node = top;        while (node != NULL)        {            cout << node->data << " ";            node = node->next;        }        cout << endl;    }}class Queue{public:    void Enqueue(Node node);    //入队    int Dequeue();              //出队    bool IsEmpty();             //是否为空private:    Stack s1;                   //用于入队    Stack s2;                   //用于出队};void Queue::Enqueue(Node node){    s1.Push(node);              //只对s1进行进栈操作    cout << "Enqueue " << node.data << endl;}int Queue::Dequeue(){    if(s2.IsEmpty())    {        if(s1.IsEmpty())        //s2和s1都为空        {            cout << "Queue Empty! Can not be dequeued again!" << endl;            exit(1);        }        else                    //s2为空s1不为空，把s1的所有元素都倒入s2中        {            while(!s1.IsEmpty())            {                int i = s1.Pop();                s2.Push(Node(i));            }        }    }    return s2.Pop();}bool Queue::IsEmpty(){    if (s1.IsEmpty() && s2.IsEmpty())    {        return 1;    }    else    {        return 0;    }}int main(){    Queue q;    q.Enqueue(Node(1));    q.Enqueue(Node(2));    q.Enqueue(Node(3));    cout << "Dequeue " << q.Dequeue() << endl;    q.Enqueue(Node(4));    cout << "Dequeue " << q.Dequeue() << endl;    cout << "Dequeue " << q.Dequeue() << endl;    cout << "Dequeue " << q.Dequeue() << endl;    return 0;}

运行结果：

Enqueue 1Enqueue 2Enqueue 3Dequeue 1Enqueue 4Dequeue 2Dequeue 3Dequeue 4Press any key to continue