c++ primer 队列模拟

         队列是一种抽象的数据类型(ADT),可以存储有序的项目序列.新项目被添加到队尾，并可以删除队首项目。队列有点像堆栈，不过堆栈在同一端进行添加和删除。这使得栈是一种先进后出(LIFO)的结构,而队列是先进先出的(FIFO)。从概念说说，队列就好比是收款台或者ATM前面排的队，所以对于上诉结构问题，队列非常合适。因此，工程的任务之一是定义个Queue类。

      队列中的项目就是顾客，Heather银行的代表介绍：通常，三分之一的顾客只需要一分钟便可获得服务，三分之一的顾客需要两分钟，另外三分之的顾客需要三分钟。

另外，顾客到达的时间是随机的，但每个小时使用自动柜员机的顾客数量相当稳定。工程的另外两个任务是：设计一个表示顾客的类；编写一个程序来模拟顾客和队列之间的交互。

      1.队列类

        首先需要设计一个Queue类。这里先列出队列的特征:

            1)队列存储有序的项目序列
            2)队列所能容纳的项目数有一定限制
            3)应当能够创建空队列
            4)应当能够检查队列是否为空
            5)应当能够检查队列是否满的

6)应当能够在队尾添加项目

7)应当能够在队首删除项目

8)应当鞥能够确定队列中项目数

        2.类设计

          1.queue.h头文件

#ifndef _QUEUE_H_#define _QUEUE_H_class Customer{private:long arrive; int processtime; public:Customer(){             arrive = processtime = 0;}void set(long when);long when() const { return arrive; }int ptime() const { return processtime; }};typedef Customer Item;class Queue{private:struct Node { Item item; struct Node *next; };enum { Q_SIZE = 10 };Node *front;Node *rear;const int qsize;Queue(const Queue & q):qsize(0){}Queue & operator=(const  Queue & q){return *this; }public:Queue(int qs = Q_SIZE);~Queue();bool isempty() const;bool isfull() const;int queuecount() const;bool enqueue(const Item &item);bool dequeue(Item &item);};#endif

2.queue.cpp

#include "StdAfx.h"#include "queue.h"#include <cstdlib>Queue::Queue(int qs):qsize(qs){front = rear = NULL;items = 0;}Queue::~Queue(){  Node *temp;  while(front != NULL)  {  temp  = front;  front = front->next;  delete temp;  }}bool Queue::isempty() const{return items == 0;}bool Queue::isfull() const{return items == qsize;}int Queue::queuecount() const{return items;}bool Queue::enqueue(const Item &item){if (isfull())         return false;Node *add = new Node();if (add == NULL)     return false; //内存不足，无法分配空间add->item = item;  //添加数据add->next = NULL;  //下一个置为空items++;           if(front == NULL)front = add;elserear->next = add; //将最后一个节点指向新分配节点rear = add;  //添加到队尾return true;}bool Queue::dequeue(Item &item){if (front == NULL)return false;item = front->item; //将首节点数据复制到引用变量中items--;Node *temp = front; //保存首节点地址front =front->next; //重置首节点指针delete temp;  if (items == 0)   rear = NULL;return true;}void Customer::set(long when){processtime = std::rand() % 3 +1;arrive = when;}

3.测试

// ch12_queue.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include "queue.h"#include <iostream>#include <ctime>const int MIN_PER_HR = 60;bool newcustomer(double x);using namespace std;int _tmain(int argc, _TCHAR* argv[]){std::srand(std::time(0));cout<<"Case Study: Bank of Heather Automatic Teller\n;";cout<<"Enter maximum size of queue: ";int qs;cin>>qs;Queue line(qs);cout<<"Enter the number of simulation hours: ";int hours;cin>>hours;long cyclelimit = MIN_PER_HR * hours;cout<<"Enter the average number of customers per hour: ";double perhour;cin>>perhour;double min_per_cust;min_per_cust = MIN_PER_HR;        Item temp;long turnaways = 0; long customers = 0;long served    = 0; long sum_line  = 0;int  wait_time = 0;long line_wait = 0;for (int cycle = 0; cycle < cyclelimit; cycle++){if (newcustomer(min_per_cust)){if (line.isfull())turnaways++;else{customers++;temp.set(cycle); //设置到达时间line.enqueue(temp);//加入队列}}if(wait_time <= 0 && !line.isempty()){line.dequeue(temp);wait_time = temp.ptime();line_wait += cycle - temp.when();served++;}if (wait_time > 0)   wait_time--;sum_line += line.queuecount();}if (customers > 0){cout<<"curtomers accepted: "<< customers<<endl;cout<<" curtomers served: " <<served <<endl;cout<<"      turnaways: "<<turnaways<<endl;cout<<"average queue size: ";cout.precision(2);cout.setf(ios_base::fixed,ios_base::floatfield);cout.setf(ios_base::showpoint);cout<<(double)sum_line / cyclelimit <<endl;cout<<" average wait time: "<<(double) line_wait / served <<" minutes\n";}elsecout<<"No customers\n";cout<<"Done\n";return 0;}bool newcustomer(double x){return (rand() * x / RAND_MAX < 1);}