链式队列

声明：图片及内容基于https://www.bilibili.com/video/av94576761

原理分析

数据结构

注意本文只考虑有头节点类型

基本数据类型

定义节点

template<class T>
struct Node {
    T data;
    struct Node<T>* next;
};

声明队列

template<class T>
class LinkQueue {
private:
    Node<T>* front, * rear;    //前后结构体指针
    int length;                //队列长度
public:
    LinkQueue();
    ~LinkQueue();
    void enQueue(T x);         //入队
    bool deQueue(T& item);     //出队
    bool getFront(T& item);    //获得头元素
    bool isEmpty();            //是否为空
    void clearQueue();         //清空队列
    void displayQueue();       //打印队列
    int queueLength();         //获得队列长度
};

队列初始化

LinkQueue<T>::LinkQueue()
{
    front = new Node<T>;
    front->next = NULL;
    rear = front;
    length = 0;         //别忘了
}

析构函数

LinkQueue<T>::~LinkQueue()
{
    struct Node<T>* p =NULL;
    while (front) {
        p = front->next;
        delete front;
        front = p;
    }
}

入队

template<class T>
void LinkQueue<T>::enQueue(T x)
{
    struct Node<T>* p = new Node<T>;
    p->data = x;
    rear->next = p;
    rear = p;
    rear->next = NULL;   //vs里必须让尾节点next=NULL否则异常
    length++;            //别忘了
}

出队

template<class T>
bool LinkQueue<T>::deQueue(T &item)
{
    if (isEmpty()) return false;
    item = front->next->data;
    struct Node<T>* p = front->next;   //front是头节点没有数据
    front->next = p->next;
    if (p->next == NULL)  rear = front; //防止只有一个元素时，其被删除后rear变为野指针
    delete p;
    length--;                          //别忘了
    return true;
}

获得头元素

template<class T>
bool LinkQueue<T>::getFront(T& item)
{
    if(isEmpty()) return false;
    item = front->next->data;         //front是头节点没有数据
    return true;
}

判断是否为空

template<class T>
bool LinkQueue<T>::isEmpty()
{
    if (front == rear) return true;
    return false;
}

清空队列

template<class T>
void LinkQueue<T>::clearQueue()
{
    struct Node<T>* p ;
    while (front) {
        p = front->next;
        delete front;
        front = p;
    }
    front = rear = NULL;       //初始化头尾指针
    length = 0;                //别忘了
}

打印队列

template<class T>
void LinkQueue<T>::displayQueue()
{    
    if (front == NULL) {              //队列为空return;
    }
    struct Node<T>* p = front->next;
    while (p!=NULL) {
        cout << p->data << " ";
        p = p->next;
    }
    cout << endl;
}

获得队列长度

template<class T>
int LinkQueue<T>::queueLength()
{
    return length;
}

完整代码

#include<iostream>
using namespace std;
template<class T>
struct Node {
    T data;
    struct Node<T>* next;
};
template<class T>
class LinkQueue {
private:
    Node<T>* front, * rear;
    int length;
public:
    LinkQueue();
    ~LinkQueue();
    void enQueue(T x);
    bool deQueue(T& item);
    bool getFront(T& item);
    bool isEmpty();
    void clearQueue();
    void displayQueue();
    int queueLength();
};

template<class T>
LinkQueue<T>::LinkQueue()
{
    front = new Node<T>;
    front->next = NULL;
    rear = front;
    length = 0;
}

template<class T>
LinkQueue<T>::~LinkQueue()
{
    struct Node<T>* p =NULL;
    while (front) {
        p = front->next;
        delete front;
        front = p;
    }
}

template<class T>
void LinkQueue<T>::enQueue(T x)
{
    struct Node<T>* p = new Node<T>;
    p->data = x;
    rear->next = p;
    rear = p;
    rear->next = NULL;   //vs里必须让尾节点next=NULL否则异常
    length++;
}

template<class T>
bool LinkQueue<T>::deQueue(T &item)
{
    if (isEmpty()) return false;
    item = front->next->data;
    struct Node<T>* p = front->next;
    front->next = p->next;
    if (p->next == NULL)  rear = front; //防止只有一个元素时rear之后变为野指针
    delete p;
    length--;
    return true;
}

template<class T>
bool LinkQueue<T>::getFront(T& item)
{
    if(isEmpty()) return false;
    item = front->next->data;
    return true;
}

template<class T>
bool LinkQueue<T>::isEmpty()
{
    if (front == rear) return true;
    return false;
}

template<class T>
void LinkQueue<T>::clearQueue()
{
    struct Node<T>* p ;
    while (front) {
        p = front->next;
        delete front;
        front = p;
    }
    front = rear = NULL;
    length = 0;
}

template<class T>
void LinkQueue<T>::displayQueue()
{    
    if (front == NULL) {
        return;
    }
    struct Node<T>* p = front->next;
    while (p!=NULL) {
        cout << p->data << " ";
        p = p->next;
    }
    cout << endl;
}

template<class T>
int LinkQueue<T>::queueLength()
{
    return length;
}
int main() {
    LinkQueue<int> Queue;
    Queue.enQueue(1);
    Queue.enQueue(2);
    Queue.enQueue(3);
    Queue.displayQueue();
    int d;
    Queue.deQueue(d);
    Queue.displayQueue();
    cout << "d=" << d << endl;
    cout << "length=" << Queue.queueLength()<<endl;
    int f;
    Queue.getFront(f);
    cout << "front=" <<f <<endl;
    Queue.clearQueue();
    if (Queue.isEmpty()) cout << "empty" << endl;
    cout << "length=" << Queue.queueLength()<<endl;
    Queue.displayQueue();
    return 0;
}