4.3 Queue

4.3 Queue

4.3.1 ADT interface

operating	Features
size()	Report the size of the queue
empty()	Determine whether the queue is empty
enqueue(e)	Insert e into the end of the line
dequeue()	Delete leader object
front()	Introduce the leader of the team

4.3.2 Queue template class

#include"List.h"
#include<iostream>
using namespace std;

template <typename T> class Queue: public List<T> {
    
     //由列表派生的队列模板类
public: //size()与empty()直接沿用
 void enqueue( T const & e ) {
    
     List<T>::insertAsLast( e ); } //入队
 T dequeue() {
    
     return List<T>::remove( List<T>::first() ); } //出队
 T & front() {
    
     return (List<T>::first())->data; } //队首
}; //以列表首/末端为队列头/尾——颠倒过来呢？

int main()
{
    
    
    Queue<int> q;
    for(int i=1;i<=10;i++){
    
    
        q.enqueue(i);
        int temp=q.front();
        cout<<i<<endl;
        q.dequeue();
    }
}

4.3.3 Application of Queue

4.3.3.1 Cyclic service simulation

RoundRobin {
    
     //循环分配器
 Queue Q( clients ); //共享资源的所有客户组成队列
 while ( ! ServiceClosed() ) {
    
     //在服务关闭之前，反复地
 e = Q.dequeue(); //令队首的客户出队，并
 serve( e ); Q.enqueue( e ); //接受服务，然后重新入队
 } }

4.3.3.2 Bank service simulation

4.3.3.2.1 Define customer objects

struct Customer {
    
     //顾客类
 int window; //所属窗口（队列）
 unsigned int time; //服务时长
};

4.3.3.2.2 Bank service simulation

void simulate( int nWin, int servTime ) {
    
     
 Queue<Customer> * windows = new Queue<Customer>[ nWin ];
 for ( int now = 0; now < servTime; now++ ) {
    
     //在下班之前，每隔单位时间
 Customer c ; c.time = 1 + rand() % 50; //一位新顾客到达，其服务时长随机指定
 c.window = bestWindow( windows, nWin ); //找出最佳（最短）服务窗口
 windows[ c.window ].enqueue( c ); //新顾客加入对应的队列
 for ( int i = 0; i < nWin; i++ ) //分别检查
 if ( ! windows[ i ].empty() ) //各非空队列
 if ( -- windows[ i ].front().time <= 0 ) //队首顾客接受服务
 windows[ i ].dequeue(); //服务完毕则出列，由后继顾客接替
 } //for
 delete [] windows; //释放所有队列
}

4.3.3.2.3 Find the shortest queue

int bestWindow(Queue<Customer>windows[],int nWin)
{
    
    
    int minSize=windows[0].size(),optiWin=0;//最优队列(窗口)
    for(int i=1;i<nWin;i++){
    
    
        if(minSize>windows[i].size())//挑选出
        {
    
    
            minSize=windows[i].size();optiWin=i;//队列最短者
        }
    }
    return optiWin;
}