queue.cpp

包括图、二叉树、链表

#include "Queue.h"

bool Queue::empty() const

/*
Post: Return true if the Queue is empty,
otherwise return false.
*/
{
	return front == NULL;
}

Queue::Queue()
/*
Post: The Queue is initialized to be empty.
*/
{
	front = rear = NULL;
}
Error_code Queue::append(const Queue_entry &item)
/*
Post: Add item to the rear of the Queue and
return a code of success or return a code
of overflow if dynamic memory is exhausted.
*/
{
	Node *new_rear = new Node(item);
	if (new_rear == NULL) return overflow;
	if (rear == NULL) front = rear = new_rear;
	else {
		rear->next = new_rear;
		rear = new_rear;
	}
	return success;
}

Error_code Queue::retrieve(Queue_entry &item) const
/*
Post: The front of the Queue is reported
in item. If the Queue
is empty return an Error_code
of underflow and leave the Queue unchanged.
*/
{
if (front == NULL) return underflow;
item = front->entry;
return success;
}

Error_code Queue::serve()
/*
Post: The front of the Queue is removed. If the Queue
is empty, return an Error_code of underflow.
*/
{
	if (front == NULL) return underflow;
	Node *old_front = front;
	front = old_front->next;
	if (front == NULL) rear = NULL;
	delete old_front;
	return success;
}
Queue::~Queue()
{
	while (!empty())
		serve();
}
Queue::Queue(const Queue &copy)
{
	Node *copy_node = copy.front;
	front = rear = NULL;
	while (copy_node != NULL) {
		append(copy_node->entry);
		copy_node = copy_node->next;
	}
}
void Queue::operator =(const Queue &copy)
{
	while (!empty())
		serve();
	Node *copy_node = copy.front;
	while (copy_node != NULL) {
		append(copy_node->entry);
		copy_node = copy_node->next;
	}
}