1. 總等待時間 VS 總顧客人數：來的顧客人多，每個人都會產生等待時間，總等待時間自然也會多，不會隨著ATM數量的增加而減少（ATM空閒情況除外）
2. 總服務人數 VS 總顧客人數：ATM增多，能同時服務的顧客人數自然更多，所以這是一個效率概念，是會有明顯提升的
3. 需要建立2個佇列用於儲存新來的顧客，但總等待時間，總服務人數，總拒絕人數都不需要單獨計算。但兩臺ATM的當前處理時間需要單獨建立，因為需要分別計算兩個佇列的dequeue()
4. 需要新增 過載operator<，用於判斷將新顧客放在哪個佇列

// queue.h -- interface for a queue
 

#ifndef QUEUE_H_
#define QUEUE_H_
// This queue will contain Customer items
class Customer
{
private:
    long arrive;        // arrival time for customer
    int processtime;    // processing time for customer
public:
    Customer() : arrive(0), processtime (0) {}
    void set(long when);
    long when() const
 

    {
        return arrive;
    }
    int ptime() const
    {
        return processtime;
    }
};

typedef Customer Item;

class Queue
{
private:
// class scope definitions
    // Node is a nested structure definition local to this class
    struct Node
    {
        Item item;
        struct Node * next;
 

    };
    enum {Q_SIZE = 10};
// private class members
    Node * front;       // pointer to front of Queue
    Node * rear;        // pointer to rear of Queue
    int items;          // current number of items in Queue
    const int qsize;    // maximum number of items in Queue
    // preemptive definitions to prevent public copying
    Queue(const Queue & q) : qsize(0) { }
    Queue & operator=(const Queue & q)
    {
        return *this;
    }
public:
    Queue(int qs = Q_SIZE); // create queue with a qs limit
    ~Queue();
    bool isempty() const;
    bool isfull() const;
    int queuecount() const;
    bool enqueue(const Item &item); // add item to end
    bool dequeue(Item &item);       // remove item from front
    // Newly Added: help distribute new customer to which queue
    bool operator<(Queue& obj);
};
#endif

// queue.cpp -- Queue and Customer methods
#include"queue.h"
#include <cstdlib>         // (or stdlib.h) for rand()


// Queue methods
Queue::Queue(int qs) : qsize(qs)
{
    front = rear = NULL;    // or nullptr
    items = 0;
}

Queue::~Queue()
{
    Node * temp;
    while (front != NULL)   // while queue is not yet empty
    {
        temp = front;       // save address of front item
        front = front->next;// reset pointer to next item
        delete temp;        // delete former front
    }
}

bool Queue::isempty() const
{
    return items == 0;
}

bool Queue::isfull() const
{
    return items == qsize;
}

int Queue::queuecount() const
{
    return items;
}

// Add item to queue
bool Queue::enqueue(const Item & item)
{
    if (isfull())
        return false;
    Node * add = new Node;  // create node
// on failure, new throws std::bad_alloc exception
    add->item = item;       // set node pointers
    add->next = NULL;       // or nullptr;
    items++;
    if (front == NULL)      // if queue is empty,
        front = add;        // place item at front
    else
        rear->next = add;   // else place at rear
    rear = add;             // have rear point to new node
    return true;
}

// Place front item into item variable and remove from queue
bool Queue::dequeue(Item & item)
{
    if (front == NULL)
        return false;
    item = front->item;     // set item to first item in queue
    items--;
    Node * temp = front;    // save location of first item
    front = front->next;    // reset front to next item
    delete temp;            // delete former first item
    if (items == 0)
        rear = NULL;
    return true;
}

bool Queue::operator<(Queue& obj)
{
    return items < obj.items;
}

// customer method

// when is the time at which the customer arrives
// the arrival time is set to when and the processing
// time set to a random value in the range 1 - 3
void Customer::set(long when)
{
    processtime = std::rand() % 3 + 1;
    arrive = when;
}

// bank.cpp -- using the Queue interface
// compile with queue.cpp
#include <iostream>
#include <cstdlib> // for rand() and srand()
#include <ctime>   // for time()
#include "queue.h"
const int MIN_PER_HR = 60;

bool newcustomer(double x); // is there a new customer?

int main()
{
    using std::cin;
    using std::cout;
    using std::endl;
    using std::ios_base;
// setting things up
    std::srand(std::time(0));    //  random initializing of rand()

    cout << "Case Study: Bank of Heather Automatic Teller\n";
    cout << "Enter maximum size of queue: ";
    int qs;
    cin >> qs;
	

    cout << "Enter the number of simulation hours: ";
    int hours;              //  hours of simulation
    cin >> hours;
    // simulation will run 1 cycle per minute
    long cyclelimit = MIN_PER_HR * hours; // # of cycles

	// clear input queue
	while (cin.get() != '\n')
		continue;
	char ch;
	cout << "Enter q to quit, others to continue.\n";
	cin.get(ch);
	while (ch != 'q')
	{
		// create 2 lines
		Queue line1(qs);         // line queue holds up to qs people
		Queue line2(qs);
		
		cout << "Enter the average number of customers per hour: ";// for 2 lines
		double perhour;         //  average # of arrival per hour
		cin >> perhour;
		double min_per_cust;    //  average time between arrivals
		min_per_cust = MIN_PER_HR / perhour;

		Item temp;              //  new customer data,OR, temp object for dequeue()
		long turnaways = 0;     //  turned away by full queue
		long customers = 0;     //  joined the queue
		long served = 0;        //  served during the simulation
		long sum_line = 0;      //  cumulative line length
		int wait_time1 = 0;      //  time until autoteller is free
		int wait_time2 = 0;
		long line_wait = 0;     //  cumulative time in line

		// running the simulation
		for (int cycle = 0; cycle < cyclelimit; cycle++)
		{
			if (newcustomer(min_per_cust))  // have newcomer
			{
				if (line1.isfull()&&line2.isfull())
					turnaways++;
				else
				{
					customers++;
					temp.set(cycle);    // cycle = time of arrival
					// Newly Added: decide which queue to put new customer into
					if (line1 < line2)
						line1.enqueue(temp); // add newcomer to line
					else
						line2.enqueue(temp);					
				}
			}
			if (wait_time1 <= 0 && !line1.isempty())
			{
				line1.dequeue(temp);      // attend next customer
				wait_time1 = temp.ptime(); // for wait_time minutes
				line_wait += cycle - temp.when();
				served++;
			}
			if (wait_time1 > 0)
				wait_time1--;
			sum_line += line1.queuecount();

			// Newly Added:same situation for line2
			if (wait_time2 <= 0 && !line2.isempty())
			{
				line2.dequeue(temp);      // attend next customer
				wait_time2 = temp.ptime(); // for wait_time minutes
				line_wait += cycle - temp.when();
				served++;
			}
			if (wait_time2 > 0)
				wait_time2--;
			sum_line += line2.queuecount();
		}

		// reporting results
		if (customers > 0)
		{
			cout << "customers accepted: " << customers << endl;
			cout << "  customers served: " << served << endl;
			cout << "         turnaways: " << turnaways << endl;
			cout << "average queue size: ";
			cout.precision(2);
			cout.setf(ios_base::fixed, ios_base::floatfield);
			cout << (double)sum_line / cyclelimit << endl;
			cout << " average wait time: "
				<< (double)line_wait / served << " minutes\n";
		}
		else
			cout << "No customers!\n";
		cout << "Done!\n";

		// clear input queue
		while (cin.get() != '\n')
			continue;
		cout << "Enter q to quit\n";
		cin.get(ch);
	}
    cin.get();
    return 0;
}

//  x = average time, in minutes, between customers
//  return value is true if customer shows up this minute
bool newcustomer(double x)
{
    return (std::rand() * x / RAND_MAX < 1); 
}