## Sunday, September 18, 2011

### Data Structure Hints

First Act

1.      What is data structure?

A data structure is a way of organizing data that considers not only the items stored, but also their relationship to each other. Advance knowledge about the relationship between data items allows designing of efficient algorithms for the manipulation of data.

2.      List out the areas in which data structures are applied extensively?
Ø  Compiler Design,
Ø  Operating System,
Ø  Database Management System,
Ø  Statistical analysis package,
Ø  Numerical Analysis,
Ø  Graphics,
Ø  Artificial Intelligence,
Ø  Simulation

3.      What are the major data structures used in the following areas : RDBMS, Network data model & Hierarchical data model.
Ø  RDBMS                         – Array  (i.e. Array of structures)
Ø  Network data model      – Graph
Ø  Hierarchical data model – Trees

4.      If you are using C language to implement the heterogeneous linked list, what pointer type will you use?
The heterogeneous linked list contains different data types in its nodes and we need a link, pointer to connect them. It is not possible to use ordinary pointers for this. So we go for void pointer. Void pointer is capable of storing pointer to any type as it is a generic pointer type.

5.      Minimum number of queues needed to implement the priority queue?
Two. One queue is used for actual storing of data and another for storing priorities.

6.      What is the data structures used to perform recursion?
Stack. Because of its LIFO (Last In First Out) property it remembers its ‘caller’ so knows whom to return when the function has to return. Recursion makes use of system stack for storing the return addresses of the function calls.
Every recursive function has its equivalent iterative (non-recursive) function. Even when such equivalent iterative procedures are written, explicit stack is to be used.

7.      What are the notations used in Evaluation of Arithmetic Expressions using prefix and postfix forms?
Polish and Reverse Polish notations.

8.      Convert the expression ((A + B) *  C – (D – E) ^ (F + G)) to equivalent Prefix and Postfix notations.
Prefix Notation:
^ - * +ABC - DE + FG
Postfix Notation:
AB + C * DE - - FG + ^
9.      Sorting is not possible by using which of the following methods?
(a) Insertion
(b) Selection
(c) Exchange
(d) Deletion

(d) Deletion.
Using insertion we can perform insertion sort, using selection we can perform selection sort, using exchange we can perform the bubble sort (and other similar sorting methods). But no sorting method can be done just using deletion.

10.  What are the methods available in storing sequential files ?
Ø  Straight merging,
Ø  Natural merging,
Ø  Polyphase sort,
Ø  Distribution of Initial runs.

11.  List out few of the Application of tree data-structure?
Ø  The manipulation of Arithmetic expression,
Ø  Symbol Table construction,
Ø  Syntax analysis.

12.  List out few of the applications that make use of Multilinked Structures?
Ø  Sparse matrix,
Ø  Index generation.

13.  In tree construction which is the suitable efficient data structure?
(a) Array           (b) Linked list              (c) Stack           (d) Queue   (e) none

14.  What is the type of the algorithm used in solving the 8 Queens problem?
Backtracking

15.  In an AVL tree, at what condition the balancing is to be done?
If the ‘pivotal value’ (or the ‘Height factor’) is greater than 1 or less than –1.

16.  What is the bucket size, when the overlapping and collision occur at same time?
One. If there is only one entry possible in the bucket, when the collision occurs, there is no way to accommodate the colliding value. This results in the overlapping of values.

17.  There are 8, 15, 13, 14 nodes were there in 4 different trees. Which of them could have formed a full binary tree?
15.
In general:
There are 2n-1 nodes in a full binary tree.
By the method of elimination:
Full binary trees contain odd number of nodes. So there cannot be full binary trees with 8 or 14 nodes, so rejected. With 13 nodes you can form a complete binary tree but not a full binary tree. So the correct answer is 15.
Note:
Full and Complete binary trees are different. All full binary trees are complete binary trees but not vice versa.

18.  Classify the Hashing Functions based on the various methods by which the key value is found.
Ø  Direct method,
Ø  Subtraction method,
Ø  Modulo-Division method,
Ø  Digit-Extraction method,
Ø  Mid-Square method,
Ø  Folding method,
Ø  Pseudo-random method.

19.  What are the types of Collision Resolution Techniques and the methods used in each of the type?
The methods used include:
Overflow block,
The methods used include:
Binary tree…

20.  In RDBMS, what is the efficient data structure used in the internal storage representation?
B+ tree. Because in B+ tree, all the data is stored only in leaf nodes, that makes searching easier. This corresponds to the records that shall be stored in leaf nodes.

21.  What is a spanning Tree?
A spanning tree is a tree associated with a network. All the nodes of the graph appear on the tree once. A minimum spanning tree is a spanning tree organized so that the total edge weight between nodes is minimized.

22.  Does the minimum spanning tree of a graph give the shortest distance between any 2 specified nodes?
No.
Minimal spanning tree assures that the total weight of the tree is kept at its minimum. But it doesn’t mean that the distance between any two nodes involved in the minimum-spanning tree is minimum.

23.  Which is the simplest file structure?
(a)   Sequential
(b)   Indexed
(c)    Random

(a) Sequential

24.  Whether Linked List is linear or Non-linear data structure?
According to Access strategies Linked list is a linear one.
According to Storage Linked List is a Non-linear one.

********************************************************************************

Short Program Logics

How would you check if a binary tree is balanced?
A tree is considered balanced when the difference between the min depth and max depth does not exceed 1.
Recursive algorithms always work well on trees, so here’s some code.
int min_depth( Node * root ) {
if( !root ) {
return 0;
}
return 1 + min( min_depth( root->left ),
min_depth( root->right ));
}

int max_depth( Node * root ) {
if( !root ) {
return 0;
}
return 1 + max( max_depth( root->left ),
max_depth( root->right ));
}

bool is_balanced( Node * root ) {
return ( max_depth( root ) - min_depth( root ) ) <= 1 }

Write a C program to determine the number of elements (or size) in a tree.
Solution:
int tree_size(struct node* node) { if (node==NULL) { return(0); } else { return(tree_size(node->left) + tree_size(node->right) + 1);
} }

Write a C program to delete a tree (i.e, free up its nodes)

Solutions:

clear(struct node* pNode)
{
if (pNode != NULL)
{
clear(pNode->left);
clear(pNode->right);
delete pNode;
}
}

Write a C program to find the depth or height of a tree.

tree_height(mynode *p) {
if(p==NULL)return(0);
if(p->left){h1=tree_height(p->left);}
if(p=>right){h2=tree_height(p->right);}
return(max(h1,h2)+1); }

The degree of the leaf is zero. The degree of a tree is the max of its element degrees. A binary tree of height n, h > 0, has at least h and at most (2^h -1) elements in it. The height of a binary tree that contains n, n>0, elements is at most n and atleast log(n+1) to the base 2.

Log(n+1) to the base 2 = h

n = (2^h - 1)

How to create a copy of a linked list? Write a C program to create a copy of a linked list.

copy_linked_lists(struct node *q, struct node **s) {
if(q!=NULL)
{
*s=malloc(sizeof(struct node));
(*s)->data=q->data;
} }

## Friday, September 9, 2011

### PHP Introduction

PHP

PHP is a powerful tool for making dynamic and interactive Web pages.
PHP is the widely-used, free, and efficient alternative to competitors such as Microsoft's ASP.

## What is PHP?

ñ PHP stands for PHP: Hypertext Preprocessor
ñ PHP is a server-side scripting language, like ASP
ñ PHP scripts are executed on the server
ñ PHP supports many databases (MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc.)
ñ PHP is an open source software

## What is a PHP File?

ñ PHP files can contain text, HTML tags and scripts
ñ PHP files are returned to the browser as plain HTML
ñ PHP files have a file extension of ".php", ".php3", or ".phtml"

## Why PHP?

ñ PHP runs on different platforms (Windows, Linux, Unix, etc.)
ñ PHP is compatible with almost all servers used today (Apache, IIS, etc.)
ñ PHP is FREE to download from the official PHP resource: www.php.net
ñ PHP is easy to learn and runs efficiently on the server side

## Where to Start?

To get access to a web server with PHP support, you can:
ñ Install Apache (or IIS) on your own server, install PHP, and MySQL
ñ Or find a web hosting plan with PHP and MySQL support

# PHP Syntax

PHP code is executed on the server, and the plain HTML result is sent to the browser.

## Basic PHP Syntax

A PHP scripting block always starts with <?php and ends with ?>. A PHP scripting block can be placed anywhere in the document.
On servers with shorthand support enabled you can start a scripting block with <? and end with ?>.
Each code line in PHP must end with a semicolon. The semicolon is a separator and is used to distinguish one set of instructions from another.

Simple “Hello World” Program

<html>
<body>

<?php
echo "Hello World";
?>

</body>
</html>

Note: The file must have a .php extension. If the file has a .html extension, the PHP code will not be executed.

# PHP Variables

Variables are used for storing values, like text strings, numbers or arrays.
When a variable is declared, it can be used over and over again in your script.
The correct way of declaring a variable in PHP:
\$var_name = value;

## PHP is a Loosely Typed Language

In PHP, a variable does not need to be declared before adding a value to it.
In the example above, you see that you do not have to tell PHP which data type the variable is.
PHP automatically converts the variable to the correct data type, depending on its value.
In a strongly typed programming language, you have to declare (define) the type and name of the variable before using it.
In PHP, the variable is declared automatically when you use it.

## The Concatenation Operator

There is only one string operator in PHP.
The concatenation operator (.)  is used to put two string values together.
To concatenate two string variables together, use the concatenation operator:

<?php
\$txt1="Hello World!";
\$txt2="What a nice day!";
echo \$txt1 . " " . \$txt2;
?>

The output of the code above will be:
Hello World! What a nice day!

# PHP Forms and User Input

The PHP \$_GET and \$_POST variables are used to retrieve information from forms, like user input.

## PHP Form Handling

The most important thing to notice when dealing with HTML forms and PHP is that any form element in an HTML page will automatically be available to your PHP scripts.

### Example

The example below contains an HTML form with two input fields and a submit button:

Name: Age:
When a user fills out the form above and click on the submit button, the form data is sent to a PHP file, called "welcome.php":
"welcome.php" looks like this:
 Welcome !
You are years old.
Output could be something like this:
 Welcome John! You are 28 years old.

Note: Highlighted \$_POST[“ “] specifies how the input value passed from another form or page is get into new PHP scripting page.

# PHP \$_GET Function

The built-in \$_GET function is used to collect values in a form with method="get".

When using method="get" in HTML forms, all variable names and values are displayed in the URL.

# PHP \$_POST Function

The built-in \$_POST function is used to collect values in a form with method="post".

Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.

Deploying our PHP Application

Windows :
Install WAMP Web-Server Software and deploy all your applications.

http://www.tinkertech.net/tutor/wamp/index.html (Refer this sites for “How to use?”)

Fedora :
Save your php files into “\var\www\html\” folder. To place your files first we have to set access permissions.
1.      Open the Terminal.
3.      Next step is to change our current working location.
4.      Type “cd ..” as many times until your present working directory(can be found by using pwd command) reaches “/”.
5.      Type cd var/www.
6.      Type “ls” it will list all the files & directories present in that directory. We have to deploy our php files under HTML.
ñ  To set access permission to HTML folder use chmod command
ñ  type chmod 777 html.
ñ  Now you have set the access permissions to that folder. We can paste any files in under that folder.

To display our PHP files in Browser,

Before opening browser, ensure that apache services is running or not.

(In Browser) Type “localhost” in url and press enter. If the apache services is running correctly, it will shows fedora test page as shown below.

If it shows “Problems on page load error” means, the apache services is not running.          open terminal (enter as super user (“su”))
ñ  Type apchectl start – to start the apache server.
ñ  Type  apchectl stop – to stop the apache server. (its not mandatory to stop).

Creating separate folders for your PHP applications

You can create any number of folders under that HTML  folder and deploy your projects without any choas by placing it under single folder.
If you put your projects in a folder named “test”, then while running it through browser, you should specify clearly as follows,

in url type, localhost/test/yourphpfilename along with .php extension

MySQL

MySQL is the most popular open-source database system.

In MySQL we can create any number of databases under particular databases we can create any number of tables.

Then type mysql.

To lists all existing databases, type show databases;

Note: Tables can be created only by selecting a database first.

To select a database, type use database_name;

to lists all tables exists under that database, type show tables;

PHP MySQL Connect to a Database

Before you can access data in a database, you must create a connection to the database. In PHP, this is done with the mysql_connect() function.

Ex :-)
<?php
\$con = mysql_connect("localhost","root","");
if (!\$con)
{
die('Could not connect: ' . mysql_error());
}

// some code

mysql_close(\$con);
?>

The connection will be closed automatically when the script ends. To close the connection before, use the mysql_close() function.

mysql_select_db() -> Sets the current active database on the server that's associated with the specified link identifier. Every subsequent call to mysql_query() will be made on the active database.

mysql_query() -> executes the INSERT INTO statement, and a new record will be added to the  table.

mysql_num_rows() -> Retrieves the number of rows from a result set. This command is only valid for statements like SELECT or SHOW that return an actual result set. To retrieve the number of rows affected by a INSERT, UPDATE, REPLACE or DELETE query, use mysql_affected_rows().

mysql_fetch_array() -> return the first row from the recordset as an array. Each call to mysql_fetch_array() returns the next row in the recordset.

Select data from database :

Ex:
mysql_select_db("my_db");

\$result = mysql_query("SELECT * FROM Persons");

while(\$row = mysql_fetch_array(\$result))
{
echo \$row['FirstName'] . " " . \$row['LastName'];
echo "<br />";
}

The while loop loops through all the records in the recordset. To print the value of each row, we use the PHP \$row variable (\$row['FirstName'] and \$row['LastName']).