/*---------------------------------------------------------
 * File Name: queuelst.cpp
 * Author: Xiannong Meng
 * Date: April 21, 1997
 * Assignment: Classroom demonstration
 * Problem statement: This is the templates file for queue class.
 *---------------------------------------------------------
 */

#include "queuelst.h"

// Queue constructor
// Intent: initialize the queue to be empty
// Precondition: none
// Postcondition: front and rear points to NULL
template <class ElmType>
Queue<ElmType>::Queue()
{
    front = rear = NULL;
}

// Insert function
// Intent: insert a node that contains value x at the rear of the queue
// Precondition: ElmType x has received values
// Postcondition: a node containing x is created and inserted into queue
template <class ElmType>
bool Queue<ElmType>::Insert(const ElmType x)
{
    Node * newNode;

    // make a new node
    newNode = new Node;
    newNode->info = x;
    newNode->link = NULL;
    
    if (IsEmpty() == true)    // first one on the list
    {
	front = newNode;
	rear  = newNode;
    }
    else                      // insert at the end
    {
	rear->link = newNode;
	rear       = newNode;
    }
    return true;
}

// Remove
// Intent: remove a node at the front of the queue, return its value to x
// Precondition: the queue should contain at least one element
// Postcondition: one node at the front is removed
template <class ElmType>
bool Queue<ElmType>::Remove(ElmType & x)
{
    if (IsEmpty() == true)
    {
	cerr << "queue empty when removing!\n";
	return false;
    }
    else
    {
	Node * temp = front;
	x = front->info;
	front = front->link;
	delete temp;
	return true;
    }
}

// IsEmpty
// Intent: test if the queue is empty, note that rear==front is not empty
// Precondition: a queue has been initialized
// Postcondition: none
template <class ElmType>
bool Queue<ElmType>::IsEmpty() const
{
    return (front == NULL);
}