Top 9 websites for practicing algorithms and Data structure.

⛓ https://www.hackerrank.com/

⛓ https://leetcode.com/

⛓ https://www.codewars.com/

⛓ https://www.hackerearth.com/for-developers

⛓ https://coderbyte.com/

⛓ https://www.coursera.org/browse/computer-science/algorithms

⛓ https://www.codechef.com/

⛓ https://codeforces.com/

⛓ https://www.geeksforgeeks.org/

Top 40 commonly asked DSA questions :

𝗔𝗿𝗿𝗮𝘆𝘀 𝗮𝗻𝗱 𝗦𝘁𝗿𝗶𝗻𝗴𝘀:
1. Find the missing number in an array of integers.
2. Implement an algorithm to rotate an array.
3. Check if a string is a palindrome.
4. Find the first non-repeating character in a string.
5. Implement an algorithm to reverse a linked list.
6. Merge two sorted arrays.
7. Implement a stack using arrays/linked list.
8. Write a program to remove duplicates from a sorted array.

𝗟𝗶𝗻𝗸𝗲𝗱 𝗟𝗶𝘀𝘁𝘀:
1. Detect a cycle in a linked list.
2. Find the intersection point of two linked lists.
3. Reverse a linked list in groups of k.
4. Implement a function to add two numbers represented by linked lists.
5. Clone a linked list with next and random pointer.

𝗧𝗿𝗲𝗲𝘀 𝗮𝗻𝗱 𝗕𝗶𝗻𝗮𝗿𝘆 𝗦𝗲𝗮𝗿𝗰𝗵 𝗧𝗿𝗲𝗲𝘀 (𝗕𝗦𝗧):
1. Find the height of a binary tree.
2. Check if a binary tree is balanced.
3. Find the lowest common ancestor in a binary tree.
4. Serialize and deserialize a binary tree.
5. Implement an algorithm for in-order traversal without recursion.
6. Convert a BST to a sorted doubly linked list.

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Here are some common frontend interview questions along with brief answers:

1. What is the DOM (Document Object Model)?
- Answer: The DOM is a programming interface for web documents. It represents the structure of a web page and allows scripts to dynamically access and update the content, structure, and style of a webpage.

2. Explain the difference between null and undefined in JavaScript.
- Answer: null represents the intentional absence of any object value, while undefined represents a variable that has been declared but has not been assigned a value.

3. What are closures in JavaScript?
- Answer: Closures are functions that remember the scope in which they were created, even after that scope has exited. They have access to variables from their containing function's scope.

4. Describe the differences between CSS Grid and Flexbox.
- Answer: CSS Grid is a two-dimensional layout system, while Flexbox is one-dimensional. Grid is used for overall layout structure, while Flexbox is ideal for distributing space and aligning items within a container along a single axis.

5. What is responsive web design, and how do you achieve it?
- Answer: Responsive web design is an approach to design and coding that makes web pages render well on various devices and screen sizes. Achieve it through media queries, flexible grids, and fluid images.

6. Explain the "box model" in CSS.
- Answer: The box model describes how elements on a web page are rendered. It consists of content, padding, border, and margin, and these properties determine the element's total size.

7. How does the event delegation work in JavaScript?
- Answer: Event delegation is a technique where you attach a single event listener to a common ancestor of multiple elements instead of attaching listeners to each element individually. Events that bubble up from child elements can be handled by the ancestor.

8. What is the purpose of the localStorage and sessionStorage objects in JavaScript?
- Answer: Both localStorage and sessionStorage allow you to store key-value pairs in a web browser. The key difference is that data stored in localStorage persists even after the browser is closed, whereas data in sessionStorage is cleared when the session ends (e.g., when the browser is closed).

9. Explain the same-origin policy in the context of web security.
- Answer: The same-origin policy is a security measure that restricts web pages from making requests to a different domain (protocol, port, or host) than the one that served the web page. It helps prevent cross-site request forgery (CSRF) and other security vulnerabilities.

10. What are the benefits of using a CSS preprocessor like Sass or Less?
- Answer: CSS preprocessors provide benefits such as variables, nesting, functions, and mixins, which enhance code reusability, maintainability, and organization. They allow you to write cleaner and more efficient CSS.

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Essential Programming Languages to Learn Data Science 👇👇

1. Python: Python is one of the most popular programming languages for data science due to its simplicity, versatility, and extensive library support (such as NumPy, Pandas, and Scikit-learn).

2. R: R is another popular language for data science, particularly in academia and research settings. It has powerful statistical analysis capabilities and a wide range of packages for data manipulation and visualization.

3. SQL: SQL (Structured Query Language) is essential for working with databases, which are a critical component of data science projects. Knowledge of SQL is necessary for querying and manipulating data stored in relational databases.

4. Java: Java is a versatile language that is widely used in enterprise applications and big data processing frameworks like Apache Hadoop and Apache Spark. Knowledge of Java can be beneficial for working with large-scale data processing systems.

5. Scala: Scala is a functional programming language that is often used in conjunction with Apache Spark for distributed data processing. Knowledge of Scala can be valuable for building high-performance data processing applications.

6. Julia: Julia is a high-performance language specifically designed for scientific computing and data analysis. It is gaining popularity in the data science community due to its speed and ease of use for numerical computations.

7. MATLAB: MATLAB is a proprietary programming language commonly used in engineering and scientific research for data analysis, visualization, and modeling. It is particularly useful for signal processing and image analysis tasks.

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