【c++版数据结构】链队列的实现

和线性表的单链表一样，为了操作方便，实现代码中链队列拥有一个头结点

该链队列：包含头指针和尾指针

代码如下：

#pragma once

#include<iostream>
#include<cstdlib>
#include<cassert>
using namespace std;

template<class T>
class Queue;

template<class T>
class QNode
{
friend Queue<T>;
private:
T _data;
QNode<T> *_next;
public:
QNode(T data = T(), QNode<T> *next = NULL) :_data(data), _next(next){}
};

template<class T>
class Queue
{
private:
QNode<T> *front;
QNode<T> *rear;
public:
explicit Queue();
virtual ~Queue();
void push(const T& value);
void pop();
bool empty()const;
size_t size()const;
T &top();
const T& top()const;
void destory();
void clear();
};

template<class T>
Queue<T>::~Queue()
{
destory();
}

template<class T>
void Queue<T>::destory()
{
clear();
delete front;
front = NULL;
rear = NULL;
}

template<class T>
void Queue<T>::clear()
{
QNode<T> *tmp = front->_next;
while (tmp != NULL)
{
front->_next = tmp->_next;
delete tmp;
tmp = front->_next;
}
}

template<class T>
const T& Queue<T>::top()const
{
assert(empty() == false);
return front->_next->_data;
}

template<class T>
T& Queue<T>::top()
{
assert(empty() == false);
return front->_next->_data;
}

template<class T>
Queue<T>::Queue()
{
front = rear = new QNode<T>;
}

template<class T>
void Queue<T>::push(const T& value)
{
QNode<T> *tmp = new QNode<T>(value);
assert(tmp != NULL);
rear->_next = tmp;
rear = rear->_next;
}

template<class T>
bool Queue<T>::empty()const
{
return front == rear;
}

template<class T>
size_t Queue<T>::size()const
{
size_t size = 0;
QNode<T> *tmp = front->_next;
while (tmp != NULL)
{
++size;
tmp = tmp->_next;
}
return size;
}

template<class T>
void Queue<T>::pop()
{
if (empty())
{
cout << "it's already empty! can't pop!" << endl;
return;
}
QNode<T> *tmp = front->_next;
front->_next = tmp->_next;
delete tmp;
if (size() == 0)
rear = front;
}