第三章 栈和队列 —— 链队列

链队列

先进先出

队列的表示和实现：

• 链队列：链式存储
• 循环队列：顺序存储

这里我们来说链队列的基本操作

• 清空链队列
• 判断链队列是否为空
• 求链队列长度
• 显示链队列队头位置元素
• 队尾入队
• 队头出队
• 显示链队列

代码如下：

#include <iostream>
#include <stdlib.h>

#define OK 1
#define ERROR -1
#define OVERFLOW -2
using namespace std;

typedef int QElemType_L;
typedef int Status;
//定义队列的结点
typedef struct QNode
{
    QElemType_L data;
    struct QNode *next;
}QNode,*QueuePtr;

//定义链队列
typedef struct
{
    QueuePtr front;//头指针
    QueuePtr rear;//尾指针
}LinkQueue;

//初始化
Status InitQueue_L(LinkQueue &Q)
{
    Q.front = Q.rear = new QNode;
    Q.front->next = NULL;
    return OK;
}

//销毁队列
Status DestoryQueue (LinkQueue &Q)
{
    while (Q.front)
    {
        Q.rear = Q.front->next;
        delete Q.front;
        Q.front = Q.rear;
    }
    return OK;
}

//清空队列
void ClearQueue_L(LinkQueue &Q)
{
    Q.rear = Q.front->next;
    while(Q.rear)
    {
        Q.front->next = Q.rear->next;
        free(Q.rear);
        Q.rear = Q.front->next;
    }
    Q.rear = Q.front;
    cout << "清空成功"<<endl;
}

//判断是否为空
void QueueEmpty_L(LinkQueue Q)
{
    if (Q.front == Q.rear)
        cout<<"链队列为空"<<endl;
    else
        cout<<"链队列不为空"<<endl;
}

//求链队列长度
int QueueLength_L(LinkQueue Q)
{
    int count = 0;
    QueuePtr p = Q.front;
    while(p!=Q.rear)
    {
        count++;
        p = p->next;
    }
    return count;
}

//显示链队列
void QueueTraverse_L(LinkQueue Q)
{
    QueuePtr p;
    p = Q.front->next;
    cout<<"链队列中的元素为：";
    while(p)
    {
        cout<<p->data<<" ";
        p = p->next;
    }
    cout<<endl;
}

//入队
Status EnQueue(LinkQueue &Q)
{
    int n,e;
    cout<<"请输入要入队的元素个数："<<endl;
    cin>>n;
    cout<<"请依次输入要入队的元素："<<endl;
    for (int i=0;i<n;i++)
    {
        cin>>e;
        QueuePtr p;
        p = (QueuePtr)malloc(sizeof(QNode));
        if(!p)
            exit(OVERFLOW);
        p->data = e;
        p->next = NULL;
        Q.rear->next = p;
        Q.rear = p;
    }
    cout<<"入队成功"<<endl;
    return OK;
}

//获取队头元素
Status GetHead_L(LinkQueue Q)
{
    QueuePtr p;
    QElemType_L e;
    if (Q.front == Q.rear)
    {
        cout<<"无队头元素"<<endl;
        return ERROR;
    }
    p = Q.front->next;
    e = p->data;
    cout<<"队头元素为："<<e<<endl;
    return OK;
}

//队头出队
Status DeQueue_L(LinkQueue &Q)
{
    QueuePtr p;
    QElemType_L e;
    if (Q.front == Q.rear)
    {
        cout<<"无队头元素"<<endl;
        return ERROR;
    }
    p = Q.front->next;
    e = p->data;
    Q.front->next = p->next;
    if(Q.rear == p)
        Q.rear = Q.front;
    free(p);
    cout << "队头元素"<<e<<"出队成功"<<endl;
    return OK;
}

void show_help()
{
    cout<<"******* Data Structure ******"<<endl;
    cout<<"1----清空链队列"<<endl;//
    cout<<"2----判断链队列是否为空"<<endl;//
    cout<<"3----求链队列长度"<<endl;//
    cout<<"4----显示链队列队头位置元素"<<endl;//
    cout<<"5----队尾入队"<<endl;//
    cout<<"6----队头出队"<<endl;//
    cout<<"7----显示链队列"<<endl;//
    cout<<"     退出，输入0"<<endl;

}
int main()
{
    int operate_code;
    show_help();
    LinkQueue Q;
    InitQueue_L(Q);
    while(1)
    {
        cout<<"";
        cin>>operate_code;
        if(operate_code==1)
        {
            ClearQueue_L(Q);
        }
        else if (operate_code==2)
        {
            QueueEmpty_L(Q);
        }
        else if (operate_code==3)
        {
            cout<<"链队列的长度为："<<QueueLength_L(Q)<<endl;
        }
        else if (operate_code==4)
        {
            GetHead_L(Q);
        }
        else if (operate_code==5)
        {
            EnQueue(Q);
        }
        else if (operate_code==6)
        {
            DeQueue_L(Q);
        }
        else if (operate_code==7)
        {
            QueueTraverse_L(Q);
        }
        else if (operate_code==0)
        {
            break;
        }
        else
        {
            cout<<"\n操作码错误！！！"<<endl;
            show_help();
        }
    }
    DestoryQueue(Q);
    return 0;
}