Notes, summaries, assignments, exams, and problems for Computer science

THE WEB:

1. WEB1.0, WEB 2.0, WEB 3.0:

-WEB 1.0 or the read-only web: In the 1990s, information on the Internet was only for reading. It was a network of documents and people could not interact with the content. For example, they couldn’t give their opinions, ask for information or register as users. In addition, the information online was not updated very frequently. Almost everything that people used online was also part of the World Wide Web (www).

WEB 2.0 or the social network:

This was developed during the first decade of the 21st century. In this new web, information became bidirectional. Users could not only receive information, but also create and share it. New services appeared and became popular, such as email, chats, videoconferences,...

TCP/IP Layering: Advantages and Drawbacks

Layering decomposes the overall communications problem into a number of more manageable sub-problems. Perhaps the major disadvantage is the processing and data overhead.

• Processing Overhead: As many as seven modules (OSI model) are invoked to move data from the application through the communications software.
• Data Overhead: This results from appending multiple headers to the data.

Another possible disadvantage is that there must be at least one protocol standard per layer. With so many layers, it takes a long time to develop and promulgate the standards.

Layering Overhead Calculation Example

A transport-layer message consisting of 2100 bits of data and 250 bits of header is sent to a network layer, which...

Set Cover to Efficient Recruiting

Input: Set U of elements, collection S₁, ..., S_m of subsets of U, integer k ≥ 0

Construct an instance of the Efficient Recruitment Problem:

• Sports are represented by U.
• Applicants are represented by {1, ..., m}.
• For every s ∈ U and 1 ≤ i ≤ m, M[s, i] = 'qualified' if s ∈ S_i and 'not qualified' otherwise.

Steps:

1. Call the oracle for Efficient Recruiting with input M and k.
2. Return the result (yes or no) of the previous call.

Vertex Cover and Hitting Set

Graph: G = (V, E)

• U = V(G)
• S_i = {u, v}, where (u, v) is an edge of G.

Vertex Cover ⇒ Hitting Set:

If C is a vertex cover for G of size k, then by definition, for every edge (u, v) in G, either u ∈ C or v ∈ C. Therefore, C is a solution for Hitting Set because...

Tree Traversal Methods

Preorder traversal: Visit the root, visit the left subtree, and then visit the right subtree.

Inorder traversal: Visit the left subtree, visit the root, and then visit the right subtree.

Postorder traversal: Visit the left subtree, visit the right subtree, and then visit the root.

Breadth-First Traversal: Visit the root, visit the children of the root (left to right), and then the children of the children (left to right), going down level by level.

Depth-First Traversal: Rather than visiting the tree level-by-level like in breadth-first traversal, visit the root, go all the way down the left on one path, and then move across the tree to the right, going down all the paths until the end.

Hashing and Collision Resolution

Hashing:

THE FILE: A file is a set of ordered documents that are related by some circumstance or event. It is essential for a company to have a file that is to sort and classify documentation in a particular way.

Why: It allows to keep, store and safeguard information, It can be easily and quickly found, To comply with the law, It can help in the decision-making process

Types of files:

1) Active: documents that are currently being used and queried

2) Semi-active: documents no longer effective but kept for legal reasons

3) Inactive: documents not valid but with a historical or documentary value

The File system: is the criterion used for ordering information.

• Alphabetical: Information classified in the order of the alphabet *

• Numerical: information in which each

Evolution of the iPhone

Released on June 29, 2007, the iPhone has seen multiple new hardware iterations with new iOS releases since.

User Interface and Connectivity

The user interface is built around the device's multi-touch screen, including a virtual keyboard. The iPhone has Wi-Fi and can connect to cellular networks.

Core iPhone Features

An iPhone can:

• Shoot video (standard feature from the iPhone 3GS)
• Take photos
• Play music
• Send and receive email
• Browse the web
• Send and receive text messages
• Follow GPS navigation
• Record notes
• Perform mathematical calculations
• Receive visual voicemail

Other functionality, such as video games, reference works, and social networking, can be enabled by downloading mobile apps.

The App Store Ecosystem

As of January 2017, Apple'...

CSS Pseudo-Class Reference

Comandos Esenciales de Iptables

• Listar reglas: iptables -t nat -L --line-numbers
• Política por defecto: iptables -t filter -P OUTPUT DROP
• Permitir HTTP e ICMP: iptables -A OUTPUT -o eth0 -p tcp --dport 80 -j ACCEPT
• Permitir Correo (25, 110): iptables -A INPUT -s 0.0.0.0/0 -p tcp --dport 25 -j ACCEPT
• Bloquear PING de IP específica: iptables -A INPUT -o eth0 -s 192.168.28.200 -p icmp -j DROP
• Redirección de puertos (80 a 8080): iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080
• DNAT (Redirección a IP): iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j DNAT --to 192.168.10.12:80
• Backup de reglas: iptables-save > mi_tabla y iptables-restore < mi_tabla
• Borrar reglas: iptables -t nat -F y iptables -D INPUT

1. Telephone communication

it has been the medium used as the first contact with a company. It is used to arrange meetings , interviews or to ask for information, so the impression of the first telephone call is very important

2. Telephone means and equipment

Fixed individual devices

Private branch exchanges (PBX):  it connects calls between two destinations or ends

Mobile devices:

PDA (Personal Digital Assistant) it`s like a small computer (Internet and electronic mail)

Smartphone:  A PDA with video, camera, radio, MP3 player  or television

Services: Internet, e-mail, videoconference, camera, audio and  Video quality player, an agenda, GPS,....

3. Additional services offered by the telephone equipment

3.1 Common features(a,b,c,)

1. Fixed telephony: -

Notice

Data Structure (Syllabus)

Semester & Branch: 3rd sem CSE/IT Teachers Assessment : 10 Marks
Theory: 4 Periods per Week Class Test : 20 Marks
Total Periods: 60 Periods per Semester End Semester Exam : 70 Marks
Examination: 3 Hours TOTAL MARKS : 100 Marks

Objective :

The effectiveness of implementation of any application in computer mainly depends on the that how effectively its information can be stored in the computer. For this purpose various -structures are used. This paper will expose the students to various fundamentals structures arrays, stacks, queues, trees etc. It will also expose the students to some fundamental, I/0 manipulation techniques like sorting, searching etc

1.0 INTRODUCTION: 04

• 1.1 Explain Data, Information, data types
• 1.2 Define