search

CS- Week 3

Jan 03, 2025 pm 07:15 PM

Algorithm is a set of instructions given in a specific sequence to solve a problem. Algorithms differ in speed and how much memory they occupy. In the programming process, most algorithms are based on data search (searching) and sorting (sorting). Let's get acquainted with data retrieval algorithms:

Linear search (Linear search)

Let us be given the following array:

[20, 500, 10, 5, 100, 1, 50]

When visualizing an array, it can be seen as seven red cabinets side by side like this:

CS- Week 3

We need to find 50 numbers from this array. The computer must check each locker to find the number 50. We call this process, that is, searching for a specific number, character or other element in an array "search".
We can pass our array to an algorithm and ask the algorithm to open the cupboards and determine if the number 50 is there. As a result, the algorithm will answer us “yes” or “no” (true or false).

CS- Week 3

We can construct an algorithm using the following instructions:

Chapdan o‘ngga har bir eshikni tekshirish:
    Agar 50 soni bor bo‘lsa:
        Ha deb qaytaramiz (return true)
Yo‘q deb qaytaramiz (return false)

The instructions above are human-readable pseudocode and are a simpler representation of the commands given to a computer.

We can implement the linear search algorithm in C using the following code:

#include <cs50.h>
#include <stdio.h>

int main(void)
{
    // Butun sonlardan iborat massiv berilgan
    int numbers[] = {20, 500, 10, 5, 100, 1, 50};

    // Kiritilgan sonni massivdan qidiramiz
    int n = get_int("Number: ");
    for (int i = 0; i 



<p>Here a linear search is performed using a for loop.<br>
return 0 means that the program has finished successfully and the program is exited.<br>
return 1 - indicates that an error occurred in the program.</p>

<hr>
<h2>
  
  
  Binary search
</h2>

<p><em>Binary Search</em> is another algorithm used to search for the number 50.<br>
If the values ​​in the array are sorted in ascending order, we can give the pseudocode of binary search as follows:<br>
</p>

<pre class="brush:php;toolbar:false">Agar tekshiriladigan element qolmagan bo‘lsa:
    Yo‘q deb qaytaramiz (return false)
Agar massivning[o‘rta elementi] 50 soniga teng bo‘lsa:
    Ha deb qaytaramiz (return true)
Agar massivning[o‘rta elementi] > 50:
    Massivning chap yarmidan qidiramiz
Agar massivning[o‘rta elementi] 




<hr>

<h2>
  
  
  Big O notation
</h2>

<p>The <strong>Big O</strong> <strong>notation</strong> is used to analyze the time it takes to run the algorithm. Let's look at the following graph: </p>

<p><img src="/static/imghwm/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/173590294458453.jpg?x-oss-process=image/resize,p_40" class="lazy" alt="CS- Week 3"></p>

<p><em>"Input data size"</em> – x-axis; <em>"Time for solution"</em> – y-axis;<br>
The efficiency of the algorithm is determined by the shape of its curve:<br>
O(n²) is the worst performance time.<br>
O(log n) is the fastest execution time.</p><p>The running time of the linear search algorithm is O(n), since in the worst case n steps may be required.<br>
And the time it takes for the binary search algorithm to work is O(log n), because in the worst case, the number of steps decreases more and more.</p>

<p>There are two cases of interest to programmers:</p>

  • Worst case or upper bound (upper bound).
  • Best case or lower bound (lower bound).
The symbol

Ω is used to denote the best case (lower bound) of the algorithm, for example Ω(n).

The symbol

TH indicates the case where the upper and lower bounds are the same, that is, the best and worst running times are the same.


Sorting algorithms (Sorting)

Sorting is the process of changing an unordered list of values ​​into ordered ones.
When an array is sorted, it is much easier for a computer to search for a specific element in it. For example, binary search (binary search) works on a sorted array but not on an unsorted array.

There are many types of sorting algorithms. Let's consider one of them selection sort (selection sort). Let us be given an array like this:

CS- Week 3

The pseudocode of the selection method algorithm is as follows:

[20, 500, 10, 5, 100, 1, 50]

Steps analysis:

  • Walking through array elements for the first time takes n - 1 steps.
  • The second time n - 2 steps are required.
  • Continuing this logic, the required steps can be expressed as:
Chapdan o‘ngga har bir eshikni tekshirish:
    Agar 50 soni bor bo‘lsa:
        Ha deb qaytaramiz (return true)
Yo‘q deb qaytaramiz (return false)

Simplifying this formula, we get: n(n-1)/2 or O(n²).
So, the algorithm of the selection method sorts in O(n²) order in the worst case. Even if all the values ​​are sorted, the number of steps does not change, so the best case is in O(n²) order.


Bubble sort algorithm (Bubble sort)

Bubble sort is another sorting algorithm where we "promote" larger values ​​ by repeatedly permuting elements.

The pseudocode of the bubble sort algorithm is as follows:

#include <cs50.h>
#include <stdio.h>

int main(void)
{
    // Butun sonlardan iborat massiv berilgan
    int numbers[] = {20, 500, 10, 5, 100, 1, 50};

    // Kiritilgan sonni massivdan qidiramiz
    int n = get_int("Number: ");
    for (int i = 0; i 



<p>As we sort the array, we know that more of it will be sorted, so we only need to check the pairs that are not yet sorted.<br>
Therefore, the bubble sort algorithm works in the worst case O(n²) if the array is not sorted, and in the best case O(n) if the array is already sorted.</p>
<p>We can see visually how the sorting algorithms work in this page.</p>

<blockquote>
<p>This article uses CS50x 2024 source.</p>
</blockquote>


          

            
        </stdio.h></cs50.h>

The above is the detailed content of CS- Week 3. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
The Continued Use of C  : Reasons for Its EnduranceThe Continued Use of C : Reasons for Its EnduranceApr 11, 2025 am 12:02 AM

C Reasons for continuous use include its high performance, wide application and evolving characteristics. 1) High-efficiency performance: C performs excellently in system programming and high-performance computing by directly manipulating memory and hardware. 2) Widely used: shine in the fields of game development, embedded systems, etc. 3) Continuous evolution: Since its release in 1983, C has continued to add new features to maintain its competitiveness.

The Future of C   and XML: Emerging Trends and TechnologiesThe Future of C and XML: Emerging Trends and TechnologiesApr 10, 2025 am 09:28 AM

The future development trends of C and XML are: 1) C will introduce new features such as modules, concepts and coroutines through the C 20 and C 23 standards to improve programming efficiency and security; 2) XML will continue to occupy an important position in data exchange and configuration files, but will face the challenges of JSON and YAML, and will develop in a more concise and easy-to-parse direction, such as the improvements of XMLSchema1.1 and XPath3.1.

Modern C   Design Patterns: Building Scalable and Maintainable SoftwareModern C Design Patterns: Building Scalable and Maintainable SoftwareApr 09, 2025 am 12:06 AM

The modern C design model uses new features of C 11 and beyond to help build more flexible and efficient software. 1) Use lambda expressions and std::function to simplify observer pattern. 2) Optimize performance through mobile semantics and perfect forwarding. 3) Intelligent pointers ensure type safety and resource management.

C   Multithreading and Concurrency: Mastering Parallel ProgrammingC Multithreading and Concurrency: Mastering Parallel ProgrammingApr 08, 2025 am 12:10 AM

C The core concepts of multithreading and concurrent programming include thread creation and management, synchronization and mutual exclusion, conditional variables, thread pooling, asynchronous programming, common errors and debugging techniques, and performance optimization and best practices. 1) Create threads using the std::thread class. The example shows how to create and wait for the thread to complete. 2) Synchronize and mutual exclusion to use std::mutex and std::lock_guard to protect shared resources and avoid data competition. 3) Condition variables realize communication and synchronization between threads through std::condition_variable. 4) The thread pool example shows how to use the ThreadPool class to process tasks in parallel to improve efficiency. 5) Asynchronous programming uses std::as

C   Deep Dive: Mastering Memory Management, Pointers, and TemplatesC Deep Dive: Mastering Memory Management, Pointers, and TemplatesApr 07, 2025 am 12:11 AM

C's memory management, pointers and templates are core features. 1. Memory management manually allocates and releases memory through new and deletes, and pay attention to the difference between heap and stack. 2. Pointers allow direct operation of memory addresses, and use them with caution. Smart pointers can simplify management. 3. Template implements generic programming, improves code reusability and flexibility, and needs to understand type derivation and specialization.

C   and System Programming: Low-Level Control and Hardware InteractionC and System Programming: Low-Level Control and Hardware InteractionApr 06, 2025 am 12:06 AM

C is suitable for system programming and hardware interaction because it provides control capabilities close to hardware and powerful features of object-oriented programming. 1)C Through low-level features such as pointer, memory management and bit operation, efficient system-level operation can be achieved. 2) Hardware interaction is implemented through device drivers, and C can write these drivers to handle communication with hardware devices.

Game Development with C  : Building High-Performance Games and SimulationsGame Development with C : Building High-Performance Games and SimulationsApr 05, 2025 am 12:11 AM

C is suitable for building high-performance gaming and simulation systems because it provides close to hardware control and efficient performance. 1) Memory management: Manual control reduces fragmentation and improves performance. 2) Compilation-time optimization: Inline functions and loop expansion improve running speed. 3) Low-level operations: Direct access to hardware, optimize graphics and physical computing.

The truth behind the C language file operation problemThe truth behind the C language file operation problemApr 04, 2025 am 11:24 AM

The truth about file operation problems: file opening failed: insufficient permissions, wrong paths, and file occupied. Data writing failed: the buffer is full, the file is not writable, and the disk space is insufficient. Other FAQs: slow file traversal, incorrect text file encoding, and binary file reading errors.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. How to Fix Audio if You Can't Hear Anyone
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
WWE 2K25: How To Unlock Everything In MyRise
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

MantisBT

MantisBT

Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

ZendStudio 13.5.1 Mac

ZendStudio 13.5.1 Mac

Powerful PHP integrated development environment

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Atom editor mac version download

Atom editor mac version download

The most popular open source editor