<?php
/**
* <p>Title: Double linked list</p>
* <p>Description: Implementation of a double linked list in PHP</p>
* @requires ListNode.php, Iterator.php and ListIterator.php
* @testscript LinkedListTest.php
* @author Oddleif Halvorsen | leif-h@online.no
* @version 1.2
*/
include_once("ListNode.php");
class LinkedList{
var $head; // reference to the first node
var $tail; // reference to the last node
var $size; // The total number of nodes
function LinkedList(){
//head and tail only points to the head and tail of the list,
//the list nodes does not point on head and tail! Hence, head and
//tail are not part of the list.
$this->head = new ListNode();
$this->tail = new ListNode();
$this->size = 0;
}
/**
* Adds a new object at a specific index, pushes
* the current further back into the list.
* @param $index Numeric value between 0 and $this->size()-1
* @param &$object A reference to the object that is to be inserted
* @return TRUE == insertino ok || FALSE == index out of bounds
*/
function addAtPosition($index, &$object){
//checks if index is not out of bounds
if($index >= 0 && $index <= $this->size()-1){
$newNode = $this->getNewNode($object);
$nodeAtIndex = &$this->getNode($index);
//new node at head
if($index == 0){
$newNode->setNext(&$nodeAtIndex);
$nodeAtIndex->setPrevious(&$newNode);
$this->head->setNext(&$newNode);
}
else //somewhere else in the list
$this->insertNodeInList(&$newNode, &$nodeAtIndex);
$this->size++;
return TRUE;
}
return FALSE;
}
/**
* Inserts a new node into a the list on a position
* where it has nodes bothe before an after.
* NOT at index 0 or $this->size()-1
* @param &$newNode A reference to the node that is inserted in the list.
* @param &$nodeAtIndex The node it is pushing away.
*/
function insertNodeInList(&$newNode, &$nodeAtIndex){
$previousNode = &$nodeAtIndex->getPrevious();
$newNode->setPrevious(&$previousNode);
$newNode->setNext(&$nodeAtIndex);
$nodeAtIndex->setPrevious(&$newNode);
$previousNode->setNext(&$newNode);
}
/**
* Create a new node,
* Appends a new node to the tail
* @param &$element The element you want to append to the list.
*/
function add(&$element){
$newNode = $this->getNewNode(&$element);
//A non empty list, mostly the case.
if(!$this->isEmpty()){
$previousNode = &$this->tail->getPrevious();
$previousNode->setNext(&$newNode);
$newNode->setPrevious(&$previousNode);
}
else //empty
$this->head->setNext(&$newNode);
$this->tail->setPrevious(&$newNode);
$this->size++;
}
/**
* Generates a new ListNode object.
* @param &$object The value of the ListNode
* @return A ListNode object
*/
function getNewNode(&$object){
return new ListNode(&$object);
}
/**
* Empties the list.
*/
function clear(){
$this->head = NULL;
$this->tail = NULL;
$this->size = 0;
}
/**
* Retrevies the object at the specified index.
* @param $index A value between 0 and $this->size()
* @return The object || FALSE == index out of bounds
*/
function get($index){
//if the list is noe empty, and the index is a legal number
if(!$this->isEmpty() && (($index >= 0) && ($index < $this->size()))){
if($index < ($this->size()/2)) //searches from head
$tmpNode = &$this->getNode($index);
else //searches from tail
$tmpNode = &$this->getNodeReversed($index);
return $tmpNode->getNodeValue();
}
//index out of bounds.
return FALSE;
}
/**
* Checks if the list is empty
* @return TRUE == empty || FALSE == not empty
*/
function isEmpty(){
return ( $this->size == 0 ? TRUE : FALSE );
}
function removeObjectAtIndex($index){
if(!$this->isEmpty() && ($index>=0 && $index<=($this->size()-1))){
$nodeToRemove = &$this->getNode($index);
switch($index){
case 0: //removing head
$nextNode = &$nodeToRemove->getNext();
$nextNode->setPrevious(NULL);
$this->head->setNext(&$nextNode);
break;
case ($this->size()-1):
//removing tail
$previousNode = &$nodeToRemove->getPrevious();
$previousNode->setNext(NULL);
$this->tail->setPrevious(&$previousNode);
break;
default:
//gets the node before and after the deleted node
$previousNode = &$nodeToRemove->getPrevious();
$nextNode = &$nodeToRemove->getNext();
//updates the references for the before and after node.
$previousNode->setNext(&$nextNode);
$nextNode->setPrevious(&$previousNode);
break;
}
//compleatly removes the node
$nodeToRemove->setPrevious(NULL);
$nodeToRemove->setNext(NULL);
//decreases the size of the list.
$this->size--;
return TRUE;
}
return FALSE;
}
/**
* Retrevies a node at a spesific index
* @param $index A value between 0 and $this->size()
* @return The node || FALSE == index out of bounds
*/
function &getNode($index){
//the list is not empty, and the index is not out of bounds
if(!$this->isEmpty() && (($index >= 0) && ($index < $this->size()))){
$tmpNode = &$this->head;
for($i=0; $i<=$index; $i++)
$tmpNode = &$tmpNode->getNext();
return $tmpNode;
}
return FALSE;
}
/**
* Retrevies the object from the tail of the list
* @param $index A value between 0 and $this->size()
* @return The node || FALSE == index out of bounds
*/
function &getNodeReversed($index){
//the list is not empty, and the index is not out of bounds
if(!$this->isEmpty() && (($index >= 0) && ($index < $this->size()))){
$tmpNode = &$this->tail;
for($i=($this->size()-1); $i>=$index; $i--)
$tmpNode = &$tmpNode->getPrevious();
return $tmpNode;
}
return FALSE;
}
/**
* Returns the size of the list
* @return The number of elements in the list
*/
function size(){
return $this->size;
}
/**
* Returns an iterator to use on the list
* @return An Iterator object, tha iterator starts on the list head.
*/
function iterator(){
include_once("Iterator.php");
return new Iterator(&$this->head, &$this);
}
/**
* Returns an ListIterator to use on the list
* @return An ListIterator object, tha iterator starts on the list head.
*/
function listIterator(){
include_once("ListIterator.php");
return new ListIterator($this->head, $this);
}
function incSize(){
$this->size++;
}
function decSize(){
$this->size--;
}
}
?>
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