Tag Archives: Technology/Internet

Friday Algorithms: A Data Structure: JavaScript Stack

algorithms, javascript, micro tutorial, web development, , , , , , , , , , , , ,

Algorithms and Data Structures

stack

Instead of writing about “pure” algorithms this time I’ve decided to write about data structures and to start with a stack implementation in JavaScript. However algorithms and data structures live together since the very beginning of the computer sciences. Another reason to write about data structures is that many algorithms need a specific data structure to be implemented. Most of the search algorithms are data structure dependent. You know that searching into a tree is different from searching into a linked list.

I’d like to write more about searching in my future algorithm posts, but first we need some data structure examples. The first one is, as I mentioned – stack.

Implemented in JavaScript this is really a simple example, which don’t need much to be understood. But in first place what is a stack?

You can thing of the “computer science” stack as a stack of sheets of paper, as it’s shown on the picture. You’ve three basic operations. You can add new element to the stack by putting it on the top of the stack, so the previous top of the stack becomes the second element in the stack. Another operation is to “pop” from the stack – remove the “first” element in the stack – the top most element, and to return it. And finally print the stack. This is difficult to define as an operation, but let say you’ve to show somehow every element from the stack.

Here’s a little diagram:

Stack

Source Code

At the end some source code:

var node = function()
{
    var data;
    var next = null;
}
 
var stack = function()
{
    this.top = null;
 
    this.push = function(data) {
        if (this.top == null) {
            this.top = new node();
            this.top.data = data;
        } else {
            var temp = new node();
            temp.data = data;
            temp.next = this.top;
            this.top = temp;
        }
    }
 
    this.pop = function() {
        var temp = this.top;
        var data = this.top.data;
        this.top = this.top.next;
        temp = null;
        return data;
    }
 
    this.print = function() {
        var node = this.top;
        while (node != null) {
            console.log(node.data);
            node = node.next;
        }
    }
}
 
var s = new stack();
 
s.push(1);
s.push(2);
s.push(3);
 
s.print();
 
var a = s.pop();
 
s.print();

Media RSS and ZF – Part 2

PHP, zend framework, , , , , , , , , , , ,

Here’s the promised chunk of code making the most simple bridge between Zend Framework and Media RSS.

Step 1

Just add a simple action in a controller:

class IndexController extends Zend_Controller_Action
{
	public function indexAction()
	{
	    $this->getResponse()->setHeader('Content-Type', 'application/xml');
	    $this->view->somevar = 'some value';
 
	    echo $this->view->render('index/index.xml');
 
	    $this->_helper->layout()->disableLayout();
	    $this->_helper->viewRenderer->setNoRender(true);
	}
}

Step 2

After you’ve setup the xml file as a view script – you can simply access it as a normal Zend Framework view:

<rss version="2.0" xmlns:media="http://search.yahoo.com/mrss/" xmlns:av="http://www.searchvideo.com/schemas/av/1.0">
  <channel>
   <title><?php echo $this->somevar ?></title>
   ...
   other media rss elements
   ...
</channel>
</rss>

Zend Framework and Media RSS

PHP, zend framework, , , , , , , , , , ,

The Problem

Since native RSS format is not designed to deliver media content, there is a need for newer format supporting video and audio. There is such format – Media RSS introduced by Yahoo! in 2004. Actually now RSS supports some king of pseudo audio and video with the enclosure tag.

Inserting Media In RSS with Media RSS

Although there is a standardized format, there is not a Zend Framework native module. There is however a proposal, but that’s far not enough.

Possible Solutions

For me there are two possible solutions. The first is writing Zend_Feed_Mrss and extend the Zend_Feed_Rss functionality, but that appears to be a non-trivial task. The second solution is to write custom view returning XML, which I’m choosing for now. I hope I can paste some code soon!

MVC in Practice: Designing Models

micro tutorial, web development, , , , , , ,

Existing Examples

Sketch

There are lots of examples online teaching you what is MVC, why it is good and how to develop an application using this pattern. However most of them use a predefined structure with already constructed database and only the connection between a database table and a model is described. Actually what happens before all this. The client tells you something he’d like to have in his application.

Just imagine the following situation. You’ve a client who tells you that he wants a blog. The blog has to have posts and users, and every user must write posts and every post must have comments. Also he wants a set of categories where each post will be attached to one ore more categories. And finally a blogroll – one ore more links to another blogs.

This is pretty general and does not pretend to be a full featured example. However the strategy to make a primary structure of the future models is to pickup the nouns in this paragraph. It is really simple:

The blog has to have posts and users, and every user must write posts and every post must have comments. Also he wants a set of categories where each post will be attached to one or more categories. And finally a blogroll – one ore more links to another blogs.

So far you can see there are five prototypes of database tables: post, user, comment, category and link.

It’s important to note that not every noun is ready to be a database table. In some cases, when the client is really smart, he can give you a more detailed description. Than there are nouns describing the other nouns, of course, they are supposed to be columns to those tables.

Every post must have title and description …

This is what we can do for now. From a raw text you can design your database and models in the MVC architecture.

Default Error Handling in Zend Framework

micro tutorial, PHP, web development, zend framework, , , , , , , ,

Zend_Controller_Action_Exception

There’s a cool feature in Zend Framework when a controller or action doesn’t exists. That’s really useful, because you simply write an ErrorController.php in you default module and every action’s exception sends the user to this controller/action and the job is done for you. What is important here is to show the error message at least on the development stage. Actually the request stores it as a parameter. Here’s some source:

<?php
 
class ErrorController extends Zend_Controller_Action
{
    public function errorAction()
    {
        $errorHandler = $this->getRequest()->getParam('error_handler');
        /* @var $error Zend_Controller_Action_Exception */
        $error = $errorHandler->exception;
        echo $error->getMessage();
    }
}