Coding Interview

Study these 45 problems well and you have prepared for 99% of your System Design Interview: 𝐄𝐚𝐬𝐲 1. Design URL Shortener like TinyURL 2. Design Text Storage Service like Pastebin 3. Design Content Delivery Network (CDN) 4. Design Parking Garage 5. Design Vending Machine 6. Design Distributed Key-Value Store 7. Design Distributed Cache 8. Design Distributed Job Scheduler 9. Design Authentication System 10. Design Unified Payments Interface (UPI) 𝐌𝐞𝐝𝐢𝐮𝐦 11. Design Instagram 12. Design Tinder 13. Design WhatsApp 14. Design Facebook 15. Design Twitter 16. Design Reddit 17. Design Netflix 18. Design Youtube 19. Design Google Search 20. Design E-commerce Store like Amazon 21. Design Spotify 22. Design TikTok 23. Design Shopify 24. Design Airbnb 25. Design Autocomplete for Search Engines 26. Design Rate Limiter 27. Design Distributed Message Queue like Kafka 28. Design Flight Booking System 29. Design Online Code Editor 30. Design Stock Exchange System 31. Design an Analytics Platform (Metrics & Logging) 32. Design Notification Service 33. Design Payment System 𝐇𝐚𝐫𝐝 34. Design Location Based Service like Yelp 35. Design Uber 36. Design Food Delivery App like Doordash 37. Design Google Docs 38. Design Google Maps 39. Design Zoom 40. Design File Sharing System like Dropbox 41. Design Ticket Booking System like BookMyShow 42. Design Distributed Web Crawler 43. Design Code Deployment System 44. Design Distributed Cloud Storage like S3 45. Design Distributed Locking Service Best DSA RESOURCES: https://topmate.io/coding/886874 All the best 👍👍

Tips for solving leetcode codings interview problems If input array is sorted then - Binary search - Two pointers If asked for all permutations/subsets then - Backtracking If given a tree then - DFS - BFS If given a graph then - DFS - BFS If given a linked list then - Two pointers If recursion is banned then - Stack If must solve in-place then - Swap corresponding values - Store one or more different values in the same pointer If asked for maximum/minimum subarray/subset/options then - Dynamic programming If asked for top/least K items then - Heap If asked for common strings then - Map - Trie Else - Map/Set for O(1) time & O(n) space - Sort input for O(nlogn) time and O(1) space

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Top 10 Java Interview Questions 1. What is Java and what are its key features? Java is a high-level, class-based, object-oriented programming language designed to have as few implementation dependencies as possible. Its key features include platform independence (write once, run anywhere), object-oriented, robustness, security, multithreading, and high performance through Just-In-Time (JIT) compiler. 2. Explain the difference between JDK, JRE, and JVM. - JDK (Java Development Kit): A full-featured software development kit required to develop Java applications, including JRE and development tools like the compiler and debugger. - JRE (Java Runtime Environment): A set of software tools for running Java applications, including JVM and libraries but no development tools. - JVM (Java Virtual Machine): An abstract machine that provides a runtime environment to execute Java bytecode, making Java platform-independent. 3. What is the difference between an abstract class and an interface in Java? - Abstract Class: Can have both abstract methods (without implementation) and concrete methods (with implementation). It can have state (instance variables). - Interface: Can only have abstract methods (Java 8 allows default and static methods). It cannot have state. An interface is implemented by classes. 4. Explain the concept of inheritance in Java. Inheritance is a mechanism in Java where one class (subclass/child class) inherits the fields and methods of another class (superclass/parent class). It promotes code reusability and establishes a parent-child relationship between classes. Inheritance is implemented using the extends keyword. 5. What is polymorphism in Java and how is it implemented? Polymorphism allows objects to be treated as instances of their parent class rather than their actual class. It can be implemented in two ways: - Compile-time polymorphism: Achieved through method overloading. - Runtime polymorphism: Achieved through method overriding. 6. How does exception handling work in Java? Exception handling in Java is managed using try, catch, finally, and throw/throws. The try block contains code that might throw an exception, catch block handles the exception, finally block executes code regardless of whether an exception occurs, and throw/throws is used to throw exceptions. 7. What is the difference between ArrayList and LinkedList in Java? - ArrayList: Implements the List interface using a dynamic array. It offers constant-time positional access but is slow for inserting or deleting elements from the middle. - LinkedList: Implements the List and Deque interfaces using a doubly-linked list. It offers faster insertions and deletions but slower positional access compared to ArrayList. 8. Explain the concept of multithreading in Java. Multithreading is a process of executing multiple threads simultaneously to maximize CPU utilization. Threads are lightweight sub-processes, and Java provides built-in support for multithreading through the java.lang.Thread class and the java.util.concurrent package. 9. What is the purpose of the final keyword in Java? The final keyword is used to define constants, prevent method overriding, and inheritance. When applied to a variable, it makes it a constant. When applied to a method, it prevents subclasses from overriding it. When applied to a class, it prevents the class from being subclassed. 10. What is garbage collection in Java and how does it work? Garbage collection is an automatic memory management feature in Java that deallocates memory occupied by objects that are no longer in use, preventing memory leaks. The JVM’s garbage collector identifies and removes these objects. Java developers can request garbage collection using System.gc(), but it is not guaranteed to run immediately. Free Resources to learn Java 👇👇 https://t.me/Java_Programming_Notes Like this post & share our channel with your loved ones: https://t.me/crackingthecodinginterview ENJOY LEARNING 👍👍

Top 10 HTML Interview Questions 1. What is HTML and what are its key features? HTML (HyperText Markup Language) is the standard language for creating web pages. Its key features include the use of tags to structure content, support for multimedia elements (like images, audio, and video), forms for user input, and the ability to link to other web pages via hyperlinks. 2. What is the difference between HTML and XHTML? HTML is more flexible with syntax rules and is not case-sensitive, while XHTML (Extensible HyperText Markup Language) is stricter, requiring elements to be properly nested, closed, and in lowercase. XHTML is an XML-based language, ensuring a more consistent and well-formed document structure. 3. What are semantic HTML elements and why are they important? Semantic HTML elements clearly describe their meaning in a human- and machine-readable way. Examples include <header>, <footer>, <article>, and <section>. They improve accessibility, SEO, and code readability by providing meaningful structure to the content. 4. How do you create a hyperlink in HTML? A hyperlink is created using the <a> (anchor) tag with the href attribute specifying the URL of the link. For example:

<a href="https://www.example.com">Visit Example</a>

5. What are HTML forms and how do you create one? HTML forms are used to collect user input and are created using the <form> tag. Forms contain various input elements like text fields, radio buttons, checkboxes, and submit buttons. For example:

<form action="/submit" method="post">
  <input type="text" name="username">
  <input type="password" name="password">
  <input type="submit" value="Submit">
</form>

6. Explain the difference between the <div> and <span> tags. The <div> tag is a block-level element used to group larger sections of content, creating distinct blocks. The <span> tag is an inline element used to group small portions of text or other inline elements. <div> typically affects the layout by creating line breaks, while <span> does not. 7. What is the purpose of the <meta> tag in HTML? The <meta> tag provides metadata about the HTML document, such as character encoding, viewport settings for responsive design, and SEO-related information like descriptions and keywords. Meta tags are placed within the <head> section of the HTML document. 8. How do you include an image in an HTML page? An image is included using the <img> tag with the src attribute specifying the path to the image file and the alt attribute providing alternative text for accessibility. For example:

<img src="image.jpg" alt="Description of image">

9. What is the difference between inline, inline-block, and block elements in HTML? - Inline elements (e.g., <span>, <a>) do not start on a new line and only take up as much width as necessary. - Block elements (e.g., <div>, <p>) start on a new line and take up the full width available. - Inline-block elements (e.g., <img>) are similar to inline elements but allow setting width and height, behaving like a combination of inline and block elements. 10. How do you embed a video in an HTML page? A video is embedded using the <video> tag with the src attribute specifying the video file. You can include optional attributes like controls for playback controls and autoplay to start playing the video automatically. For example:

<video src="video.mp4" controls>
  Your browser does not support the video tag.
</video>

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Top 10 SQL Interview Questions 1. What is SQL and what are its key features? SQL (Structured Query Language) is a standard language for managing and manipulating relational databases. Its key features include data querying, data manipulation (inserting, updating, deleting), data definition (creating and altering tables), and data control (granting and revoking permissions). 2. What are the differences between SQL and NoSQL databases? SQL databases are relational, table-based databases with a predefined schema, ideal for structured data and complex queries. NoSQL databases are non-relational, can be document-based, key-value pairs, wide-column stores, or graph databases, and are suitable for unstructured data and flexible schema requirements. 3. Explain the difference between a primary key and a foreign key. A primary key is a unique identifier for a record in a table, ensuring that no two rows have the same primary key value. A foreign key is a field (or a collection of fields) in one table that uniquely identifies a row in another table, establishing a relationship between the two tables. 4. What are SQL joins and what are the different types? SQL joins are used to combine rows from two or more tables based on a related column. The different types of joins include: - INNER JOIN: Returns records with matching values in both tables. - LEFT JOIN: Returns all records from the left table and matched records from the right table. - RIGHT JOIN: Returns all records from the right table and matched records from the left table. - FULL JOIN: Returns all records when there is a match in either left or right table. 5. How do you use the GROUP BY clause in SQL? The GROUP BY clause is used to group rows that have the same values in specified columns into summary rows. It is often used with aggregate functions (COUNT, SUM, AVG, MAX, MIN) to perform operations on each group of rows. 6. What is a subquery and how is it used in SQL? A subquery is a query nested within another query. It can be used in SELECT, INSERT, UPDATE, or DELETE statements to perform operations based on the results of the subquery. Subqueries can return individual values or sets of rows. 7. Explain the difference between DELETE and TRUNCATE in SQL. DELETE removes specific rows from a table based on a condition and can be rolled back. TRUNCATE removes all rows from a table, is faster, uses fewer resources, and cannot be rolled back (in most RDBMS). 8. What is a SQL View and how do you create one? A view is a virtual table based on the result set of a SELECT query. It allows users to simplify complex queries, encapsulate logic, and secure data. A view is created using the CREATE VIEW statement:

CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

9. How do you optimize SQL queries for better performance? SQL query optimization can be achieved through several methods, including: - Using proper indexing. - Avoiding unnecessary columns in SELECT statements. - Using joins instead of subqueries where appropriate. - Analyzing and rewriting complex queries for efficiency. - Ensuring statistics are up-to-date. 10. What is a stored procedure and how do you create one in SQL? A stored procedure is a set of SQL statements that can be executed as a single unit. It is used to encapsulate repetitive tasks, improve performance, and enhance security. A stored procedure is created using the CREATE PROCEDURE statement:

CREATE PROCEDURE procedure_name
AS
BEGIN
    -- SQL statements
END;

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Top 10 JavaScript Interview Questions 1. What is JavaScript and what are its key features? JavaScript is a high-level, interpreted programming language primarily used for web development. Its key features include being event-driven, prototype-based, dynamically typed, and having first-class functions. It supports functional, object-oriented, and imperative programming styles. 2. What are the differences between JavaScript and Java? JavaScript is an interpreted language, primarily used for web development to create interactive effects within web browsers. Java, on the other hand, is a compiled, statically-typed programming language used for building applications that run on the Java Virtual Machine (JVM). JavaScript is dynamically typed, whereas Java requires explicit declaration of variable types. 3. Explain the difference between let, var, and const in JavaScript. - var is function-scoped and can be redeclared and updated. - let is block-scoped and can be updated but not redeclared within the same scope. - const is block-scoped and cannot be updated or redeclared, but the properties of objects declared with const can be modified. 4. What is a closure in JavaScript? A closure is a function that retains access to its lexical scope, even when the function is executed outside that scope. This allows the function to access variables from its defining scope even after that scope has finished executing. 5. How do you handle asynchronous operations in JavaScript? Asynchronous operations in JavaScript can be handled using callbacks, Promises, or async/await. Callbacks are functions passed as arguments to other functions, Promises represent eventual completion or failure of an asynchronous operation, and async/await allows writing asynchronous code that looks synchronous. 6. What is the Document Object Model (DOM) and how do you manipulate it using JavaScript? The DOM is a programming interface for HTML and XML documents, representing the structure of a document as a tree of objects. JavaScript can manipulate the DOM using methods like getElementById(), querySelector(), createElement(), and properties like innerHTML and style. 7. Explain the difference between == and === in JavaScript. The == operator performs type coercion, meaning it converts the operands to the same type before comparing them. The === operator, on the other hand, does not perform type coercion and compares both value and type directly. 8. What is the event loop in JavaScript? The event loop is a mechanism that allows JavaScript to perform non-blocking, asynchronous operations. It continuously checks the call stack and the message queue. If the call stack is empty, it takes the first event from the message queue and pushes it to the call stack, allowing asynchronous callbacks to be executed. 9. How do you create and use a JavaScript module? JavaScript modules can be created using the export keyword to export functions, objects, or primitives from a file, and the import keyword to import them into another file. This promotes modular code and reuse of functionality across different parts of an application. 10. How do you handle errors in JavaScript? Errors in JavaScript can be handled using try-catch blocks. The code that may throw an error is placed in the try block, and any exceptions are caught and handled in the catch block. Additionally, a finally block can be used to execute code regardless of whether an exception occurs. You can check these resources for Coding interview Preparation Credits: https://t.me/free4unow_backup All the best 👍👍

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