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;
};

intmain()
{
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：

01 2 3 4 5 6 7 8 9

1.1

hello

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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：

Enqueue1

Enqueue2

Enqueue3

Dequeue1

Enqueue4

Dequeue2

Dequeue3

Dequeue4

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