code-diesel » algorithms

Doubly Linked List in php

sameer — Mon, 13 Jul 2009 11:43:40 +0000

Below is a non circular doubly linked list php implementation. I do not frequently encounter linked-list coding in practice, but doing it just for the fun of it feels nice; also helps to brush up on those data structure theories.


 
/* doublelist.class.php */
 
class ListNode {
 
    public $data;
    public $next;
    public $previous;
 
    function __construct($data) {
        $this->data = $data;
    }
 
    public function readNode() {
        return $this->data;
    }
 
}
 
 
class DoublyLinkedList {
 
    private $_firstNode;
    private $_lastNode;
    private $_count;
 
    function __construct() {
        $this->_firstNode = NULL;
        $this->_lastNode = NULL;
        $this->_count = 0;
    }
 
    public function isEmpty() {
        return ($this->_firstNode == NULL);
    }
 
    public function insertFirst($data) {
        $newLink = new ListNode($data);
 
        if($this->isEmpty()) {
            $this->_lastNode = $newLink;
        } else {
            $this->_firstNode->previous = $newLink;
        }
 
        $newLink->next = $this->_firstNode;
        $this->_firstNode = $newLink;
        $this->_count++;
    }
 
 
    public function insertLast($data) {
        $newLink = new ListNode($data);
 
        if($this->isEmpty()) {
            $this->_firstNode = $newLink;
        } else {
            $this->_lastNode->next = $newLink;
        }
 
        $newLink->previous = $this->_lastNode;
        $this->_lastNode = $newLink;
        $this->_count++;
    }
 
 
    public function insertAfter($key, $data) {
        $current = $this->_firstNode;
 
        while($current->data != $key) {
            $current = $current->next;
 
            if($current == NULL)
                return false;
        }
 
        $newLink = new ListNode($data);
 
        if($current == $this->_lastNode) {
            $newLink->next = NULL;
            $this->_lastNode = $newLink;
        } else {
            $newLink->next = $current->next;
            $current->next->previous = $newLink;
        }
 
        $newLink->previous = $current;
        $current->next = $newLink;
        $this->_count++;
 
        return true;
    }
 
 
    public function deleteFirstNode() {
 
        $temp = $this->_firstNode;
 
        if($this->_firstNode->next == NULL) {
            $this->_lastNode = NULL;
        } else {
            $this->_firstNode->next->previous = NULL;
        }
 
        $this->_firstNode = $this->_firstNode->next;
        $this->_count--;
        return $temp;
    }
 
 
    public function deleteLastNode() {
 
        $temp = $this->_lastNode;
 
        if($this->_firstNode->next == NULL) {
            $this->firtNode = NULL;
        } else {
            $this->_lastNode->previous->next = NULL;
        }
 
        $this->_lastNode = $this->_lastNode->previous;
        $this->_count--;
        return $temp;
    }
 
 
    public function deleteNode($key) {
 
        $current = $this->_firstNode;
 
        while($current->data != $key) {
            $current = $current->next;
            if($current == NULL)
                return null;
        }
 
        if($current == $this->_firstNode) {
            $this->_firstNode = $current->next;
        } else {
            $current->previous->next = $current->next;
        }
 
        if($current == $this->_lastNode) {
            $this->_lastNode = $current->previous;
        } else {
            $current->next->previous = $current->previous;
        }
 
        $this->_count--;
        return $current;
    }
 
 
    public function displayForward() {
 
        $current = $this->_firstNode;
 
        while($current != NULL) {
            echo $current->readNode() . " ";
            $current = $current->next;
        }
    }
 
 
    public function displayBackward() {
 
        $current = $this->_lastNode;
 
        while($current != NULL) {
            echo $current->readNode() . " ";
            $current = $current->previous;
        }
    }
 
    public function totalNodes() {
        return $this->_count;
    }
 
}
 
 
?>

PHPUnit Test:


 
require_once 'doublelist.class.php';
require_once 'PHPUnit/Framework.php';
 
class LinkListTest extends PHPUnit_Framework_TestCase {
 
    public function testLinkList() {
 
        $totalNodes = 100;
 
        $theList = new DoublyLinkedList();
 
        for($i=1; $i <= $totalNodes; $i++) {
            $theList->insertLast($i);
        }
 
        $this->assertEquals($totalNodes, $theList->totalNodes());
 
        for($i=1; $i <= $totalNodes; $i++) {
            $theList->insertFirst($i);
        }
 
        $totalNodes = $totalNodes * 2;
        $this->assertEquals($totalNodes, $theList->totalNodes());
 
        $theList->deleteFirstNode(); $totalNodes--;
        $this->assertEquals($totalNodes, $theList->totalNodes());
 
        $theList->deleteLastNode(); $totalNodes--;
        $this->assertEquals($totalNodes, $theList->totalNodes());
 
        /* Delete node which has a key value of '50' */
        $theList->deleteNode(50); $totalNodes--;
        $this->assertEquals($totalNodes, $theList->totalNodes());
 
        /* Insert a node at the end of the list with a value of '22' */
        $theList->insertLast(22); $totalNodes++;
        $this->assertEquals($totalNodes, $theList->totalNodes());
 
    }
}
 
?>

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Finding if an array is ordered

sameer — Thu, 08 Jan 2009 11:19:30 +0000

I recently wrote a quick code to find if a numeric array is ordered i.e sorted in a ascending or descending order. I needed it to check a sort algorithm I had written. The problem is that the following code has a worst-case running time of O(N). Can we make the running time logarithmic.

/* orderedArray.php */
 
define("ORDER_ASC", 1);
define("ORDER_DSC", 0);
 
function is_array_ordered($array, $sort_order)
{
    $i=0;
    $total_elements = count($array);
 
    if($sort_order == ORDER_ASC)
    {
        //Check for ascending order
        while($total_elements > 1)
        {
            if($array[$i] < $array[$i+1]) 
            {
                $i++;
                $total_elements--;
            }
            else
            {
                return false;
            }
        }
    }
    elseif($sort_order == ORDER_DSC)
    {
        //Check for descending order
        while($total_elements > 1)
        {
            if($array[$i] > $array[$i+1]) 
            {
                $i++;
                $total_elements--;
            }
            else
            {
                return false;
            }
        }
    }
 
    return true;
}

The unit test for the same is given below.

include 'PHPUnit/Framework.php';
include 'orderedArray.php';
 
class ArrayTest extends PHPUnit_Framework_TestCase
{
    public function testArrayOrder()
    {
        // Ascending
        $test_array = array(0,1,2,3,4,6,7,8,9,10);
        $this->assertEquals(is_array_ordered($test_array, ORDER_ASC), true);
 
        $test_array = array(10,9,8,7,6,5,4,3,2,1,0);
        $this->assertEquals(is_array_ordered($test_array, ORDER_ASC), false);
 
        $test_array = array(0,1,2,3,4,6,7,8,9,10,1);
        $this->assertEquals(is_array_ordered($test_array, ORDER_ASC), false);
 
        $test_array = array(1,0,1,2,3,4,6,7,8,9,10);
        $this->assertEquals(is_array_ordered($test_array, ORDER_ASC), false);
 
 
        // Descending
        $test_array = array(10,9,8,7,6,5,4,3,2,1,0);
        $this->assertEquals(is_array_ordered($test_array, ORDER_DSC), true);
 
        $test_array = array(0,1,2,3,4,6,7,8,9,10);
        $this->assertEquals(is_array_ordered($test_array, ORDER_DSC), false);
 
        $test_array = array(10,9,8,7,6,5,4,3,2,1,0,1);
        $this->assertEquals(is_array_ordered($test_array, ORDER_DSC), false);
 
        $test_array = array(1,10,9,8,7,6,5,4,3,2,1,0);
        $this->assertEquals(is_array_ordered($test_array, ORDER_DSC), false);
 
    }
}

Linked List implementation in PHP

sameer — Tue, 24 Jun 2008 17:24:02 +0000

Data structures are one of the core elements of computer science and they are also fun to program. But being a web developer the opportunity for implementing them in any application is quite rare. But then I thought, What the heck! I can just code for the joy of it, and it will also help me brush up on my DS skills. So here it is, a single linked list implementation in PHP for whoever may care. I will be posting other data structure and algorithm implementations here, so keeping watching. The code is given below.

CODE:


 
/** 
* Title: Single linked list
* Description: Implementation of a single linked list in PHP 
* @author Sameer Borate | codediesel.com
* @version 1.0 20th June 2008
*/
 
class ListNode
{
    /* Data to hold */
    public $data;
 
    /* Link to next node */
    public $next;
 
 
    /* Node constructor */
    function __construct($data)
    {
        $this->data = $data;
        $this->next = NULL;
    }
 
    function readNode()
    {
        return $this->data;
    }
}
 
 
class LinkList
{
    /* Link to the first node in the list */
    private $firstNode;
 
    /* Link to the last node in the list */
    private $lastNode;
 
    /* Total nodes in the list */
    private $count;
 
 
 
    /* List constructor */
    function __construct()
    {
        $this->firstNode = NULL;
        $this->lastNode = NULL;
        $this->count = 0;
    }
 
    public function isEmpty()
    {
        return ($this->firstNode == NULL);
    }
 
    public function insertFirst($data)
    {
        $link = new ListNode($data);
        $link->next = $this->firstNode;
        $this->firstNode = &$link;
 
        /* If this is the first node inserted in the list
           then set the lastNode pointer to it.
        */
        if($this->lastNode == NULL)
            $this->lastNode = &$link;
 
        $this->count++;
    }
 
    public function insertLast($data)
    {
        if($this->firstNode != NULL)
        {
            $link = new ListNode($data);
            $this->lastNode->next = $link;
            $link->next = NULL;
            $this->lastNode = &$link;
            $this->count++;
        }
        else
        {
            $this->insertFirst($data);
        }
    }
 
    public function deleteFirstNode()
    {
        $temp = $this->firstNode;
        $this->firstNode = $this->firstNode->next;
        if($this->firstNode != NULL)
            $this->count--;
 
        return $temp;
    }
 
    public function deleteLastNode()
    {
        if($this->firstNode != NULL)
        {
            if($this->firstNode->next == NULL)
            {
                $this->firstNode = NULL;
                $this->count--;
            }
            else
            {
                $previousNode = $this->firstNode;
                $currentNode = $this->firstNode->next;
 
                while($currentNode->next != NULL)
                {
                    $previousNode = $currentNode;
                    $currentNode = $currentNode->next;
                }
 
                $previousNode->next = NULL;
                $this->count--;
            }
        }
    }
 
    public function deleteNode($key)
    {
        $current = $this->firstNode;
        $previous = $this->firstNode;
 
        while($current->data != $key)
        {
            if($current->next == NULL)
                return NULL;
            else
            {
                $previous = $current;
                $current = $current->next;
            }
        }
 
        if($current == $this->firstNode)
            $this->firstNode = $this->firstNode->next;
        else
            $previous->next = $current->next;
 
        $this->count--;   
    }
 
    public function find($key)
    {
        $current = $this->firstNode;
        while($current->data != $key)
        {
            if($current->next == NULL)
                return null;
            else
                $current = $current->next;
        }
        return $current;
    }
 
    public function readNode($nodePos)
    {
        if($nodePos <= $this->count)
        {
            $current = $this->firstNode;
            $pos = 1;
            while($pos != $nodePos)
            {
                if($current->next == NULL)
                    return null;
                else
                    $current = $current->next;
 
                $pos++;
            }
            return $current->data;
        }
        else
            return NULL;
    }
 
    public function totalNodes()
    {
        return $this->count;
    }
 
    public function readList()
    {
        $listData = array();
        $current = $this->firstNode;
 
        while($current != NULL)
        {
            array_push($listData, $current->readNode());
            $current = $current->next;
        }
        return $listData;
    }
 
    public function reverseList()
    {
        if($this->firstNode != NULL)
        {
            if($this->firstNode->next != NULL)
            {
                $current = $this->firstNode;
                $new = NULL;
 
                while ($current != NULL)
                {
                    $temp = $current->next;
                    $current->next = $new;
                    $new = $current;
                    $current = $temp;
                }
                $this->firstNode = $new;
            }
        }
    }
}
 
?>
?>

PHPUnit test :


 
require_once 'linklist.class.php';
require_once 'PHPUnit/Framework.php';
 
class LinkListTest extends PHPUnit_Framework_TestCase
{
    public function testLinkList()
    {
 
        $totalNodes = 100;
 
        $theList = new LinkList();
 
        for($i=1; $i <= $totalNodes; $i++)
        {
            $theList->insertLast($i);
        }
 
        $this->assertEquals($totalNodes, $theList->totalNodes());
 
        for($i=1; $i <= $totalNodes; $i++)
        {
            $theList->insertFirst($i);
        }
 
        $totalNodes = $totalNodes * 2;
        $this->assertEquals($totalNodes, $theList->totalNodes());
 
        $theList->reverseList();
        $this->assertEquals($totalNodes, $theList->totalNodes());
 
        $theList->deleteFirstNode();
        $this->assertEquals($totalNodes - 1, $theList->totalNodes());
 
        $theList->deleteLastNode();
        $this->assertEquals($totalNodes - 2, $theList->totalNodes());
 
        /* Delete node which has a value of '5' */
        $theList->deleteNode(5);
        $this->assertEquals($totalNodes - 3, $theList->totalNodes());
 
        /* Insert a node at the end of the list with a value of '22' */
        $theList->insertLast(22);
        $this->assertEquals($totalNodes - 2, $theList->totalNodes());
 
        /* Find a node with a value of '25' (is in the list) */
        $found = $theList->find(25);
        $this->assertEquals(25, $found->data);
 
        /* Find a node with a value of '125' (is not in the list) */
        $found = $theList->find(125);
        $this->assertNull($found);
 
        /* Return the data stored in the node at position '50'
           which is in the list */
        $data = $theList->readNode(50);
        $this->assertEquals(50, $data);
 
        /* Return the data stored in the node at position '450'
           which is not in the list */
        $data = $theList->readNode(450);
        $this->assertNull($data);
    }
}
 
?>

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