Modify or rewrite the Queue class (Display 13.21 through 13.23) to simulate cust
ID: 3598882 • Letter: M
Question
Modify or rewrite the Queue class (Display 13.21 through 13.23) to simulate
customer arrivals at the Department of Motor Vehicles (DMV) counter.
As customers arrive, they are given a ticket number starting at 1 and
incrementing with each new customer. When a customer service agent is
free, the customer with the next ticket number is called. This system results
in a FIFO queue of customers ordered by ticket number. Write a program
that implements the queue and simulates customers entering and leaving
the queue. Input into the queue should be the ticket number and a
timestamp when the ticket was entered into the queue. A ticket and its corresponding
timestamp is removed when a customer service agent handles
the next customer. Your program should save the length of time the last
three customers spent waiting in the queue. Every time a ticket is removed
from the queue, update these times and output the average of the last three
customers as an estimate of how long it will take until the next customer is
handled. If nobody is in the queue, output that the line is empty.
Code to compute a timestamp based on the computer’s clock is given
below. The time(NULL) function returns the number of seconds since
January 1, 1970, on most implementations of C++:
#include <ctime>
...
int main()
{
long seconds;
seconds = static_cast<long>(time(NULL));
cout << "Seconds since 1/1/1970: " << seconds << endl;
return 0;
}
Sample execution is shown here:
The line is empty.
Enter '1' to simulate a customer's arrival, '2' to help the
next customer, or '3' to quit.
1
Customer 1 entered the queue at time 100000044.
Enter '1' to simulate a customer's arrival, '2' to help the
next customer, or '3' to quit.
1
Customer 2 entered the queue at time 100000049.
Enter '1' to simulate a customer's arrival, '2' to help the
next customer, or '3' to quit.
1
Customer 3 entered the queue at time 100000055.
Enter '1' to simulate a customer's arrival, '2' to help the
next customer, or '3' to quit.
2
Customer 1 is being helped at time 100000069. Wait time = 25
seconds.
The estimated wait time for customer 2 is 25 seconds.
Enter '1' to simulate a customer's arrival, '2' to help the
next customer, or '3' to quit.
2
Customer 2 is being helped at time 100000076. Wait time = 27
seconds.
The estimated wait time for customer 3 is 26 seconds.
Enter '1' to simulate a customer's arrival, '2' to help the
next customer, or '3' to quit.
1
Customer 4 entered the queue at time 100000080.
Enter '1' to simulate a customer's arrival, '2' to help the
next customer, or '3' to quit.
2
Customer 3 is being helped at time 100000099. Wait time = 44
seconds.
The estimated wait time for customer 4 is 32 seconds.
Explanation / Answer
#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
#define MAX_SIZE 100
class Queue{
private:
int data[MAX_SIZE];
long timestamp[MAX_SIZE];
long time_a, time_b, time_c;
int removed;
int front;
int rear;
public:
Queue(){
front = -1;
rear = -1;
time_a=0;time_b=0;time_c=0;
removed=0;
}
void Enqueue(int element, long time){
if ( Size() == MAX_SIZE - 1 ){
cout << "Queue is full" << endl;
return;
}
data[rear] = element;
timestamp[rear] = time;
rear = ++rear % MAX_SIZE;
cout << "Customer " << element << " entered the queue at time " << time << "." << endl;
}
void Dequeue(){
long now = static_cast<long>(time(NULL));
if ( isEmpty() ){
cout << "Queue is empty" << endl;
return;
}
long ret = timestamp[front];
long wait_time = now - ret;
cout << "Customer "<<data[front]<<" is being helped at time "<<ret<<". Wait time = "<<wait_time<<" seconds." << endl;
time_c = time_b;
time_b = time_a;
time_a = wait_time;
front = ++front % MAX_SIZE;
removed++;
if(front==rear){
cout << "Queue is empty" << endl;
}else{
long avg_wait_time = (time_a+time_b+time_c)/3.0;
if(removed==1){
avg_wait_time = time_a;
}else if(removed==2){
avg_wait_time = (time_a+time_b)/2.0;
}
cout << "The estimated wait time for customer "<<data[front]<<" is "<<avg_wait_time<<" seconds." << endl;
}
}
int Front(){
if ( isEmpty() ){
cout << "Queue is empty" << endl;
return -1;
}
return data[front];
}
int Size(){
return abs(rear - front);
}
bool isEmpty(){
return ( front == rear ) ? true : false;
}
};
int main(){
int command, counter=1;
long time_stamp;
Queue q;
while(true){
cout << "Enter '1' to simulate a customer's arrival, '2' to help the next customer, or '3' to quit." << endl;
cin >> command;
if(command==3){break;}
if(command==1){
time_stamp = static_cast<long>(time(NULL));
q.Enqueue(counter++, time_stamp);
}else{
q.Dequeue();
}
}
}
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