队列课下作业

作业要求

用链表实现队列需补全：

dequeue()方法
声明一个泛型，首先判断是否为空；当链表中只有一个元素时，将front的元素赋给result，使其为null；当不只一个时，将front引用指向下一个节点，并使总数count--

public T dequeue() throws EmptyCollectionException {
        if (isEmpty()) throw new EmptyCollectionException("queue");
        T result = front.getElement();
        front = front.getNext();
        count--;
        if (isEmpty()) rear = null;
        return result;

first()方法
直接返回front.getElement()

public T first() throws EmptyCollectionException {
        if (isEmpty()) throw new EmptyCollectionException("queue");
        return front.getElement();
    }

isEmpty()

返回count == 0 的布尔值
public boolean isEmpty() {
        return (count == 0);
    }

size()
返回count的值

public int size() {
        return count;
    }

toString()
将每个元素历遍，toString的结果相加

public String toString() {
        String result = "";
        LinearNode<T> current = front;
        while (current != null) {
            result = result + (current.getElement()).toString() + "\n";
            current = current.getNext();
        }
        return result;
    }

Java实现

public class TicketCounter {
    final static int PROCESS = 120;
    final static int MAX_CASHIERS = 10;
    final static int NUM_CUSTOMERS = 100;

    public static void main(String[] args) {
        Customer customer;
        LinkedQueue<Customer> customerQueue = new LinkedQueue<Customer>();
        int[] cashierTime = new int[MAX_CASHIERS];
        int totalTime, averageTime, departs;      /** process the simulation for various number of cashiers */
        for (int cashiers = 0; cashiers < MAX_CASHIERS; cashiers++) {          /** set each cashiers time to zero initially*/
            for (int count = 0; count < cashiers; count++) cashierTime[count] = 0;         /** load customer queue */
            for (int count = 1; count <= NUM_CUSTOMERS; count++) customerQueue.enqueue(new Customer(count * 15) {

                public void deposit() {

                }
            });
            totalTime = 0;         /** process all customers in the queue */while (!(customerQueue.isEmpty())) {
                for (int count = 0; count <= cashiers; count++) {
                    if (!(customerQueue.isEmpty())) {
                        customer = customerQueue.dequeue();
                        if (customer.getArrivalTime() > cashierTime[count])
                            departs = customer.getArrivalTime() + PROCESS;
                        else departs = cashierTime[count] + PROCESS;
                        customer.setDepartureTime(departs);
                        cashierTime[count] = departs;
                        totalTime += customer.totalTime();
                    }
                }
            }         /** output results for this simulation */averageTime = totalTime / NUM_CUSTOMERS;
            System.out.println("Number of cashiers: " + (cashiers + 1));
            System.out.println("Average time: " + averageTime + "\n");
        }
    }
}

单步跟踪

测试结果

代码链接

队列变化图

不太理解题目要求