Questions
Core Programming Concepts (Basics)
1. What is a variable? How do you declare one in your favorite language?
A variable is a named storage that holds data. In JavaScript, you declare one using let x = 5; or const y = "text";.
2. What is the difference between == and === in JavaScript?
== compares values after type coercion, while === compares both value and type strictly without coercion.
3. Explain the concept of immutability.
Immutability means once a data structure is created, it cannot be altered. Operations produce new copies rather than modifying the original, leading to predictable behavior and easier debugging.
4. What is a function? How is it different from a method?
A function is a reusable block of code. A method is a function tied to an object or class, operating on the data contained within that object.
5. What is recursion? Provide an example.
Recursion is when a function calls itself.
Example in JavaScript:
6. Explain pass-by-value and pass-by-reference.
Pass-by-value copies the actual value to the function, so changes don’t affect the original. Pass-by-reference passes the address, so modifications affect the original object.
7. What are primitive data types in your language of choice?
In JavaScript: Number, String, Boolean, Null, Undefined, Symbol, and BigInt.
8. How do you swap two variables without using a temporary variable?
Using destructuring in JavaScript:
9. What are null and undefined?
null is an intentional assignment for no value. undefined means a variable has been declared but not assigned a value.
10. What is the difference between a stack and a queue?
A stack is LIFO (last-in, first-out) while a queue is FIFO (first-in, first-out).
Object-Oriented Programming (OOP)
1. What is the difference between a class and an object?
A class is a blueprint for creating objects. An object is an instance of a class containing actual data.
2. Define encapsulation.
Encapsulation bundles data and methods operating on that data within a class, restricting direct access to some components to protect integrity.
3. What is inheritance? Provide an example.
Inheritance allows a class to acquire properties and methods from another.
Example:
4. What is polymorphism?
Polymorphism lets methods do different things based on the object they are acting on, typically through method overriding.
5. What are abstract classes?
Abstract classes cannot be instantiated and often contain abstract methods that must be implemented by subclasses.
6. What is the difference between an interface and an abstract class?
An interface defines a contract with no implementation, while an abstract class can provide base implementations and state.
7. How does method overloading differ from method overriding?
Overloading: same method name, different parameters in the same class. Overriding: subclass provides a specific implementation of a method defined in a superclass.
8. What are getters and setters? Why are they useful?
Getters and setters are methods to read/write property values, allowing control over how properties are accessed or modified.
9. Explain the purpose of constructors in classes.
Constructors initialize new objects, setting up initial state and resource allocation.
10. What is multiple inheritance, and why can it be problematic?
Multiple inheritance allows a class to inherit from multiple classes. It can cause ambiguity (diamond problem) and increased complexity.
Data Structures
1. How does a hash table work?
It uses a hash function to map keys to indices in an array, allowing fast insertion, deletion, and lookup.
2. What are the differences between an array and a linked list?
Arrays have fixed size, contiguous memory, fast access by index. Linked lists have dynamic size, non-contiguous memory, slow random access but fast insertions/deletions.
3. How does a binary search tree differ from a binary tree?
A binary search tree (BST) orders nodes: left child < parent < right child, enabling efficient search.
4. What is a graph? Explain directed vs. undirected graphs.
A graph is a set of nodes connected by edges. Directed graphs have one-way edges; undirected graphs have bidirectional edges.
5. What is a stack, and where is it used?
A stack is a LIFO structure used in function call management, expression evaluation, and backtracking algorithms.
6. What is a circular linked list?
A circular linked list’s last node points back to the first, forming a loop.
7. Explain a heap and its applications.
A heap is a tree-based structure satisfying the heap property (max or min). Used in priority queues and heap sort.
8. What is a trie, and how is it used?
A trie is a tree for efficient retrieval of keys, often used for autocomplete and dictionary implementations.
9. What is a priority queue?
A priority queue is an abstract data type where each element has a priority, and elements are dequeued based on priority.
10. How do you balance a binary search tree?
Through algorithms like AVL or Red-Black trees that perform rotations to maintain height balance.
Algorithms
1. What is the difference between breadth-first search (BFS) and depth-first search (DFS)?
BFS explores neighbors level by level. DFS dives deep along a branch before backtracking.
2. How do you find the maximum subarray sum?
Use Kadane’s algorithm to iterate and track local and global maximum sums.
3. Explain the divide-and-conquer approach with an example.
Divide problem into subproblems, solve recursively, and combine. Example: Merge sort splits arrays, sorts halves, and merges them.
4. What is the time complexity of binary search?
O(log n)
5. What is dynamic programming? Provide an example.
It's solving problems by combining solutions to subproblems, storing results to avoid redundancy. Example: Fibonacci with memoization.
6. How would you reverse a linked list?
Iterate through the list adjusting pointers.
7. How do you find duplicates in an array?
Use a hash set to track seen elements; duplicates appear when adding fails.
8. Write pseudocode to sort an array using merge sort.
9. Explain the concept of memoization.
Memoization caches function results by input to avoid repeated calculations for the same inputs.
10. How would you check if a string is a palindrome?
Compare the string to its reverse. If equal, it's a palindrome.
Database
1. What is normalization in databases?
Process of structuring data to reduce redundancy and improve integrity through normal forms.
2. What are the differences between primary key and foreign key?
Primary key uniquely identifies a record. A foreign key references a primary key in another table establishing relations.
3. How does indexing work?
Indexes create a data structure to quickly locate rows, speeding up queries at the cost of extra storage and slower writes.
4. What is a stored procedure?
A saved set of SQL statements on the database server to perform operations, improving performance and reusability.
5. Explain ACID properties in a database.
Atomicity, Consistency, Isolation, Durability – guarantees reliable transactions.
6. What are the differences between SQL and NoSQL databases?
SQL uses structured schema and relational tables. NoSQL is schema-less, uses various models (document, key-value, etc.), and scales horizontally.
7. How do you perform a join in SQL?
Using JOIN clauses to combine rows from two or more tables based on a related column.
8. What is sharding, and why is it used?
Sharding partitions data across multiple databases or servers to improve scalability and performance.
9. What is a deadlock in database transactions?
A situation where two or more transactions permanently block each other by holding locks the others need.
10. How do you optimize a slow SQL query?
Use proper indexing, query refactoring, analyzing execution plans, and adjusting schema design.
System Design
1. How do you design a URL shortener like Bitly?
Use a database for mappings, encode IDs into short strings, handle collisions, and scale with caching and sharding.
2. What is load balancing, and how does it work?
Distributes network or application traffic across servers to ensure reliability and efficiency.
3. What is a microservices architecture?
Breaks an app into loosely coupled, independently deployable services focused on specific functions.
4. How would you handle rate limiting in an API?
Implement counters or token buckets per user/IP with time windows, using middleware or API gateways.
5. Explain the CAP theorem.
In a distributed system, you can only guarantee two of three: Consistency, Availability, Partition tolerance.
6. What is caching, and how do you implement it?
Store frequently accessed data temporarily in a fast storage layer to reduce load times. Use in-memory caches like Redis or browser caches.
7. How would you design a distributed file storage system?
Use replicated storage nodes, metadata servers, consistent hashing, and fault tolerance strategies.
8. What are the differences between monolithic and distributed systems?
Monolithic: single codebase, tightly coupled. Distributed: multiple services, decoupled, scalable independently.
9. How would you design a messaging queue system?
Use producers, consumers, brokers with persistence, ordering guarantees, and scaling via partitioning.
10. What are some techniques for database scaling?
Vertical scaling, horizontal sharding, replication, caching, and load balancing.
Web Development
1. What is the difference between frontend and backend development?
Frontend deals with UI/UX in the browser; backend handles server logic, databases, and APIs.
2. Explain the DOM.
The Document Object Model is a tree structure representing HTML/XML documents, allowing programmatic access.
3. What is CORS, and why does it exist?
Cross-Origin Resource Sharing defines how browsers and servers share resources across different origins securely.
4. What is the purpose of cookies, local storage, and session storage?
They store client-side data: cookies for small data with HTTP support; localStorage for persistent key-value data; sessionStorage for data lasting a browser session.
5. What are the differences between HTTP and HTTPS?
HTTPS adds encryption (TLS/SSL) to HTTP for secure data transmission.
6. What are WebSockets?
A protocol for full-duplex communication channels over a single TCP connection, enabling real-time data exchange.
7. How do you prevent XSS attacks?
Sanitize user input, encode outputs, use Content Security Policies, and avoid inline scripts.
8. What is the difference between client-side and server-side rendering?
Client-side rendering generates HTML in the browser using JavaScript. Server-side rendering produces complete HTML on the server for faster initial load and SEO.
9. Explain how a REST API works.
Uses HTTP methods (GET, POST, PUT, DELETE) to manipulate resources identified by URLs, statelessly exchanging data typically in JSON.
10. What is GraphQL, and how does it differ from REST?
GraphQL is a query language for APIs allowing clients to request exactly the data they need, reducing over-fetching compared to REST.
Security
1. What is SQL injection, and how can it be prevented?
A code injection attack using malicious SQL. Prevent by using parameterized queries, ORM frameworks, and input validation.
2. What is cross-site scripting (XSS)?
Injection of malicious scripts into webpages viewed by others. Prevent by escaping outputs and validating inputs.
3. How do you securely store passwords?
Hash passwords with a strong algorithm (bcrypt, Argon2) and salt them to protect against brute force.
4. What is a man-in-the-middle attack?
An attacker intercepts communication between two parties to steal or alter data. Mitigate with encryption and certificate validation.
5. What is token-based authentication?
Use tokens (JWTs, OAuth tokens) to verify identity instead of sessions, enabling stateless authentication.
6. How does HTTPS secure communication?
Uses TLS/SSL to encrypt data between client and server, ensuring confidentiality and integrity.
7. What is the purpose of OAuth?
OAuth authorizes third-party apps to access user data without sharing credentials, using token delegation.
8. What is CSRF, and how can it be prevented?
Cross-Site Request Forgery tricks users into submitting unwanted actions. Prevent with CSRF tokens, same-site cookies, and validation.
9. Explain public key cryptography.
Uses paired keys: public for encryption/verification, private for decryption/signing, enabling secure communication without shared secrets.
10. What are JWTs (JSON Web Tokens), and how are they used?
JWTs are compact, self-contained tokens that transmit information securely between parties, often used for authentication.
DevOps & Tools
1. What is CI/CD?
Continuous Integration/Continuous Deployment: automated building, testing, and deploying software for rapid delivery.
2. How does Docker work?
Docker packages applications and dependencies into containers using OS-level virtualization for consistency across environments.
3. What is Kubernetes, and why is it used?
An orchestration tool for automating deployment, scaling, and management of containerized applications.
4. Explain the purpose of a reverse proxy.
A reverse proxy forwards client requests to backend servers, adding load balancing, caching, security, and abstraction.
5. What is the difference between scaling vertically and horizontally?
Vertical scaling increases resources of a single machine; horizontal scaling adds more machines to distribute load.
6. What is infrastructure as code?
Managing and provisioning infrastructure using code and automation tools, ensuring reproducibility and version control.
7. How do you monitor server health?
Use metrics (CPU, memory, disk usage), logs, uptime checks, and monitoring tools like Prometheus, Grafana, or New Relic.
8. What are the benefits of using a cloud provider like AWS?
Scalability, reliability, diverse services, pay-as-you-go, and global infrastructure without hardware management.
9. How would you debug a failing deployment?
Check logs, monitor resource usage, verify configurations, use version control to rollback, and isolate issues methodically.
10. What are environment variables, and why are they important?
Configuration values set outside code, allowing separation of configuration from code and secure management of secrets.
Advanced Topics
1. What is a race condition?
A flaw where outcomes depend on the timing of threads/processes, leading to unpredictable results.
2. How do you handle deadlocks?
Avoid circular wait by ordering resource acquisition, use timeouts, lock hierarchies, or deadlock detection algorithms.
3. What is event-driven programming?
A paradigm where flow is determined by events (user actions, messages), and handlers respond to these asynchronously.
4. What is garbage collection in programming?
Automatic reclamation of memory by identifying and freeing objects no longer in use.
5. Explain the purpose of design patterns like Singleton or Factory.
They provide reusable solutions to common design problems—Singleton ensures a single instance; Factory abstracts object creation.
6. How do you profile and optimize performance in an application?
Use profiling tools to identify bottlenecks, optimize algorithms, refactor code, and use caching or concurrency where needed.
7. What is multithreading, and how do you manage thread safety?
Running multiple threads concurrently. Ensure safety with locks, mutexes, atomic operations, and avoiding shared mutable state.
8. What is the purpose of a message broker?
A mediator that routes messages between services, decoupling systems, improving scalability and reliability.
9. How does a blockchain work at a high level?
A decentralized ledger where transactions are grouped in blocks, linked cryptographically, and validated by consensus.
10. What is eventual consistency, and where is it used?
A consistency model where updates propagate gradually, so all nodes eventually converge. Used in distributed databases for high availability.
Programming Fundamentals
1. What are constants, and how are they different from variables?
Constants are immutable values that cannot be reassigned after declaration. Variables can change their value over time.
2. Explain the difference between compilation and interpretation.
Compilation translates source code to machine code before execution. Interpretation executes code line by line at runtime without producing a separate machine code file.
3. How do you define a function in your language of choice?
In JavaScript:
4. What is the purpose of the return statement in a function?
It exits the function and optionally returns a value to the caller.
5. What are default parameters in a function?
Default parameters assign a default value to a function parameter if no argument is provided.
6. Explain the difference between while and for loops.
A while loop runs until a condition is false, often used when iteration count is unknown. A for loop is typically used for a known number of iterations.
7. What is a ternary operator?
A shorthand conditional operator: condition ? exprIfTrue : exprIfFalse.
8. How do you handle type conversion in your preferred language?
In JavaScript, use functions like Number(), String(), or Boolean() for explicit conversion.
9. What are higher-order functions?
Functions that take other functions as arguments or return functions as results.
10. What is a lambda or anonymous function?
A function defined without a name, often used as a callback. In JavaScript:
Intermediate Programming Concepts
1. How does a switch statement work?
It compares a value against multiple cases and executes corresponding code blocks until a break is encountered.
2. What is a callback function?
A function passed as an argument to another function to be executed later.
3. What are closures in programming?
A closure is a function that captures variables from its surrounding scope even after that scope has finished executing.
4. Explain the difference between deep copy and shallow copy.
A shallow copy duplicates only the top-level structure; nested objects are shared. A deep copy replicates all nested structures, creating independent copies.
5. What is tail recursion?
A recursion where the recursive call is the last operation in the function, enabling optimization by reusing stack frames.
6. What is the difference between synchronous and asynchronous programming?
Synchronous code executes sequentially, blocking further execution until complete. Asynchronous code allows other operations to run while waiting for tasks to complete.
7. What are named and optional arguments?
Named arguments explicitly specify parameter names during function calls. Optional arguments are parameters with default values, not required in every call.
8. Explain the purpose of the yield keyword.
yield pauses a generator function, returning a value and preserving state for resumption.
9. How do you implement a custom iterator?
Define an object with a next() method returning { value, done } or implement [Symbol.iterator]() returning such an object in JavaScript.
10. What is a generator function?
A function that can pause execution (yield) and resume later, producing a sequence of values.
Data Structures (Different Perspective)
1. What is a deque, and how does it work?
A deque (double-ended queue) allows insertion and removal from both ends.
2. Explain the difference between singly and doubly linked lists.
Singly linked lists have nodes with a pointer to the next node. Doubly linked lists have pointers to both next and previous nodes.
3. What is an adjacency matrix?
A 2D array representing graph edges, where matrix[i][j] indicates edge presence between vertices i and j.
4. How do you traverse a tree level by level?
Use breadth-first search (BFS) with a queue to process nodes level by level.
5. What is a hash collision, and how do you resolve it?
When two keys hash to the same index. Resolutions include chaining (linked lists) or open addressing (probing).
6. What is a skip list?
A probabilistic data structure that allows fast search by maintaining multiple linked lists at different levels to skip through elements.
7. How does a self-balancing tree like AVL work?
AVL trees rebalance after insertions/deletions using rotations, maintaining height differences ≤1 between subtrees.
8. What is a B-tree, and where is it used?
A balanced tree optimized for disk reads/writes, used in databases and file systems to handle large data blocks.
9. How do you detect a cycle in a linked list?
Use Floyd’s Tortoise and Hare algorithm: two pointers moving at different speeds; if they meet, there's a cycle.
10. What is the difference between immutable and mutable data structures?
Immutable structures cannot be altered after creation; mutable ones can change state.
Algorithms (Variety)
1. How does bubble sort work?
Repeatedly steps through the list, compares adjacent elements, and swaps them if out of order until sorted.
2. What is quicksort, and why is it efficient?
A divide-and-conquer sort that partitions data around a pivot, sorting subarrays recursively. It's efficient due to average-case O(n log n) time.
3. Explain Dijkstra’s algorithm.
An algorithm for finding the shortest path in a weighted graph by iteratively selecting the closest unvisited vertex and updating distances.
4. How do you find the shortest path in an unweighted graph?
Use breadth-first search (BFS), which finds the shortest path in terms of edges.
5. Write pseudocode for binary search.
6. What is the purpose of a greedy algorithm?
It makes locally optimal choices at each step aiming for a global optimum.
7. What is the difference between Prim’s and Kruskal’s algorithms?
Both find minimum spanning trees: Prim’s grows one tree, picking minimum edges from the tree to new vertices; Kruskal’s sorts edges and adds them if they don’t form a cycle, potentially creating a forest.
8. How would you find the longest common substring of two strings?
Use dynamic programming to build a table of common suffix lengths or suffix tree/trie for optimized search.
9. What is the Floyd-Warshall algorithm?
A dynamic programming algorithm for finding shortest paths between all pairs of vertices in a weighted graph.
10. Explain backtracking with an example.
Backtracking tries possible solutions recursively, undoing choices if they lead to dead ends. Example: solving a maze by exploring paths and backtracking upon hitting walls.
Object-Oriented Programming (Different Viewpoints)
1. What is a mixin?
A mixin is a class providing methods that can be used by other classes without using inheritance, adding reusable functionality.
2. What is the purpose of a static method?
A static method belongs to the class itself, not instances, used for utility functions related to the class.
3. How do you implement a singleton pattern?
Ensure a class has only one instance and provide a global access point:
4. What is a decorator in OOP?
A design pattern that adds behavior to objects dynamically without altering their structure.
5. How does polymorphism improve code flexibility?
It allows objects of different classes to be treated as instances of a common superclass, enabling interchangeable use and easier code extension.
6. What is duck typing, and which languages use it?
Duck typing determines an object’s suitability by methods/properties rather than type. Languages like Python and JavaScript use duck typing.
7. What are virtual functions?
In OOP languages like C++, virtual functions allow derived classes to override methods to provide specialized behavior.
8. Explain the difference between composition and inheritance.
Inheritance models “is-a” relationships, extending classes. Composition models “has-a” relationships, building complex types by combining simpler ones.
9. What is method chaining?
A technique where methods return the object itself, allowing multiple method calls in a single statement:
10. How do you handle diamond inheritance issues?
Use interfaces or mixins, or languages with virtual inheritance (C++) to avoid duplicate base class instances.
Web Development (Variety)
1. How does the internet work?
A global network of interconnected devices using standardized protocols (TCP/IP) to send/receive data.
2. What is a web server?
A system that hosts websites and serves web pages to clients via HTTP/HTTPS.
3. Explain the difference between a GET and POST request.
GET requests retrieve data, typically idempotent; POST submits data to be processed, causing state changes.
4. What is a status code in HTTP? Provide examples.
Numeric codes indicating request outcome. Examples:
- 200 OK (success)
- 404 Not Found (resource missing)
- 500 Internal Server Error (server fault)
5. How does a browser render a webpage?
It downloads HTML, CSS, JS, constructs the DOM and CSSOM, applies styles, executes scripts, and paints pixels on screen.
6. What are HTML, CSS, and JavaScript?
HTML structures content, CSS styles it, and JavaScript adds interactivity.
7. What is the difference between inline, internal, and external CSS?
Inline CSS applies styles directly in an element. Internal CSS is defined in a <style> block in HTML. External CSS resides in separate files linked to HTML.
8. What is the box model in CSS?
A layout model consisting of content, padding, border, and margin defining element size and spacing.
9. How does a browser’s event loop work?
It continuously checks the call stack and callback queue, executing tasks sequentially to handle asynchronous events without blocking.
10. What is DOM manipulation?
Changing the Document Object Model via scripts to alter webpage content, structure, or style dynamically.
Advanced Topics
1. What are design principles like SOLID?
SOLID principles (Single Responsibility, Open-Closed, Liskov Substitution, Interface Segregation, Dependency Inversion) guide maintainable, scalable OOP design.
2. What is the observer pattern?
A design pattern where subjects maintain a list of observers notified of state changes.
3. How does reactive programming work?
It builds systems reacting to data streams and propagation of change, often using observables and event streams.
4. What is the difference between a monad and a functor?
A functor applies a function over wrapped values. A monad extends a functor with the ability to chain operations that return wrapped values.
5. What is the purpose of memoization in functional programming?
To cache function results for given inputs, avoiding repeated calculations and improving performance.
6. What are pure functions?
Functions that return the same output for the same inputs and cause no side effects.
7. How do you implement event sourcing?
Capture all changes as events, storing them sequentially, and reconstruct state by replaying events.
8. What is eventual consistency, and why is it important?
A model where updates propagate over time, ensuring all nodes converge eventually—crucial for availability in distributed systems.
9. Explain the concept of immutability in functional programming.
Data is never modified after creation; instead, new data structures are created for changes, ensuring predictability.
10. What is lazy evaluation?
Deferring computation until its result is needed, potentially improving performance by avoiding unnecessary calculations.
Database (Advanced)
1. What is a materialized view?
A stored query result that can be refreshed, providing faster read performance at the cost of storage.
2. How does indexing improve query performance?
Indexes allow quick lookup of rows matching criteria, reducing full table scans.
3. What is the difference between a clustered and non-clustered index?
A clustered index sorts and stores data rows in the table based on key values. A non-clustered index stores pointers to the data rows.
4. How do you enforce constraints in a database?
Using SQL constraints like PRIMARY KEY, FOREIGN KEY, UNIQUE, CHECK, and NOT NULL to enforce rules on data.
5. What are triggers in SQL?
Special procedures automatically executed in response to certain events on a table or view.
6. What is the difference between row-level and column-level locking?
Row-level locks restrict individual rows; column-level locking restricts specific columns, though less common.
7. How do you perform database migrations?
Use migration tools/scripts to version and apply schema changes incrementally without data loss.
8. What is database replication?
Copying and maintaining database objects in multiple databases for redundancy and high availability.
9. Explain the difference between vertical and horizontal partitioning.
Vertical partitioning splits a table by columns. Horizontal partitioning divides rows across tables or databases.
10. What is the purpose of database transactions?
To group multiple operations into a single, atomic unit of work, ensuring ACID properties.
System Design (Advanced)
1. What is a content delivery network (CDN)?
A distributed network of servers delivering cached web content to users based on geographic proximity, improving speed and reliability.
2. How do you design a rate limiter?
Implement counters or token buckets per user/IP with time windows to limit request rates, using in-memory stores or distributed caches.
3. What is a distributed hash table?
A decentralized system providing a lookup service, mapping keys to values across nodes, enabling scalable peer-to-peer networks.
4. How would you design a search engine?
Crawl web pages, index content, rank results, and handle queries efficiently using distributed systems and algorithms.
5. What are API gateways?
Service that sits between clients and microservices, handling request routing, composition, authentication, rate limiting, and protocol translation.
6. How do you handle failover in distributed systems?
Implement redundancy, health checks, automatic switching to backup systems, and data replication to ensure continuity.
7. What is data consistency, and how do you achieve it?
Ensuring all users see the same data across systems. Achieve with transactions, consensus algorithms, or consistency models like strong or eventual consistency.
8. How do you implement fault tolerance?
Design systems to continue operation despite failures using redundancy, graceful degradation, retries, and fallback mechanisms.
9. What is quorum in distributed systems?
A minimum number of nodes required to agree on an operation, ensuring consistency and reliability in distributed consensus.
10. How do you design a logging system?
Centralize logs from services, use structured formats, aggregate with collectors, store in scalable storage, and provide search/analysis tools.
DevOps & Tools (Different)
1. What is a build pipeline?
An automated sequence of steps to compile, test, and package code, ensuring reliable software builds.
2. How do you containerize an application?
Use Docker to create an image with the app and dependencies, defining behavior in a Dockerfile, then run containers from that image.
3. What is Helm in Kubernetes?
A package manager for Kubernetes, using charts to define, install, and upgrade complex Kubernetes applications.
4. How does a service mesh work?
A dedicated infrastructure layer managing service-to-service communication, handling routing, security, and observability without modifying application code.
5. What are the benefits of serverless computing?
Abstract server management, automatic scaling, pay-per-use billing, and focus on code rather than infrastructure.
6. How do you implement blue-green deployment?
Maintain two identical environments (blue & green), switch traffic from old to new version seamlessly after deployment, reducing downtime.
7. What is a monitoring stack, and what tools are commonly used?
A set of tools to collect, visualize, and alert on system metrics/logs. Common tools: Prometheus, Grafana, ELK stack (Elasticsearch, Logstash, Kibana).
8. How does Terraform differ from Ansible?
Terraform focuses on provisioning and managing infrastructure as code. Ansible is used for configuration management and orchestration tasks.
9. How do you manage secrets in a DevOps pipeline?
Use vault services (HashiCorp Vault, AWS Secrets Manager), environment variables secured in CI/CD, and encrypted secret storage.
10. What is the 12-factor app methodology?
A set of principles for building scalable, maintainable web apps, emphasizing codebase, dependencies, config, backing services, build/release/run, processes, port binding, concurrency, disposability, dev/prod parity, logs, and admin processes.
Programming Fundamentals
1. What are constants in programming, and why are they used?
Constants are fixed values that cannot be changed during program execution. They improve code readability, maintainability, and prevent accidental modifications.
2. How does integer overflow occur?
When an arithmetic operation exceeds the maximum representable value of an integer type, the value wraps around, leading to incorrect results.
3. What is the purpose of a type system?
A type system enforces constraints on the kinds of data that can be used, catching errors early, improving code reliability, and aiding documentation and optimization.
4. What is the difference between a strongly typed and weakly typed language?
Strongly typed languages enforce strict type rules, reducing unexpected behavior. Weakly typed languages allow more implicit type conversions, which can lead to subtle bugs.
5. Explain the difference between compile-time and runtime errors.
Compile-time errors are detected during code compilation (syntax errors, type mismatches). Runtime errors occur during program execution (null reference, division by zero).
6. What is an enum, and where is it useful?
An enum defines a set of named constants, making code more readable and less error-prone when dealing with a fixed set of related values.
7. How do you check if a number is even or odd programmatically?
Use modulo operator:
8. What are global variables, and why are they discouraged?
Global variables are accessible throughout the program. They are discouraged due to potential naming conflicts, unintended side effects, and maintenance difficulties.
9. What is a type alias?
A type alias gives a new name to an existing type, improving code readability and abstraction without creating new types.
10. How does short-circuit evaluation work?
Logical operators (&&, ||) evaluate operands left-to-right and stop as soon as the outcome is determined, skipping unnecessary evaluations.
Intermediate Programming Concepts
1. What is the difference between a thread and a process?
A process is an independent execution unit with its own memory space; a thread is a lightweight unit of execution within a process sharing its memory.
2. How do you reverse a string in your preferred language?
In JavaScript:
3. What is tail-call optimization?
An optimization that reuses stack frames for tail-recursive calls, preventing stack overflow and reducing memory usage.
4. How do you implement a stack using an array?
Use array methods: push() to add elements (push) and pop() to remove elements (pop), following LIFO order.
5. What is the difference between mutable and immutable objects?
Mutable objects can change after creation; immutable objects cannot, ensuring state consistency.
6. What is the purpose of the finally block in exception handling?
The finally block executes code regardless of exceptions, used for cleanup tasks like closing files or releasing resources.
7. How do you implement a circular queue?
Use an array with pointers for head and tail that wrap around when reaching the end, managing enqueue/dequeue operations accordingly.
8. What are bitwise operators, and where are they used?
Operators that perform bit-level manipulation (&, |, ^, ~, <<, >>). They are used in low-level programming, optimizations, and bit flags.
9. How do you check for memory leaks in an application?
Use profiling tools, monitor memory usage over time, check for unreleased resources, and analyze heap snapshots to identify leaks.
10. What is the difference between synchronous and blocking calls?
Synchronous calls wait for completion before proceeding. Blocking calls halt execution until they finish, which may occur in synchronous or asynchronous contexts.
Object-Oriented Programming
1. What is a destructor, and when is it called?
A destructor is a method invoked when an object is about to be destroyed, used to release resources.
2. How do you create an abstract method in your language of choice?
In Java, declare an abstract method in an abstract class:
3. What are access modifiers, and why are they important?
Access modifiers (public, private, protected) control visibility of class members, enforcing encapsulation and protecting data integrity.
4. What is dependency injection?
A design pattern where dependencies are provided to a class rather than created inside it, enhancing testability and flexibility.
5. How do you achieve method overriding in your language?
Subclass defines a method with the same signature as in the parent class, optionally using annotations (e.g., @Override in Java).
6. Explain the concept of "composition over inheritance."
Favoring building classes by composing objects with desired behaviors over inheriting from parent classes, promoting flexibility and modularity.
7. What is a virtual destructor, and why is it needed?
A virtual destructor ensures proper resource cleanup when deleting an object through a base class pointer, crucial in polymorphic classes.
8. What are final classes or methods?
Classes/methods declared final cannot be subclassed/overridden, enforcing immutability of behavior and structure.
9. How does the concept of "open/closed principle" work in OOP?
Software entities should be open for extension but closed for modification, allowing new features without altering existing code.
10. What are object pooling and its benefits?
Object pooling reuses instances instead of creating new ones, improving performance, reducing memory churn, and lowering garbage collection overhead.
Data Structures
1. What is a min heap, and how is it implemented?
A min heap is a binary tree where the parent is less than or equal to its children. It's implemented using arrays with algorithms for insertion (bubble-up) and removal (bubble-down).
2. How do you traverse a binary tree in post-order?
Visit left subtree, then right subtree, then root.
3. What is the difference between adjacency lists and adjacency matrices?
Adjacency list: each vertex stores a list of neighbors. Adjacency matrix: 2D array indicating edges between vertex pairs.
4. How do you detect a cycle in a directed graph?
Use depth-first search (DFS) with recursion stack tracking. If a node is revisited in the current path, a cycle exists.
5. What is a Bloom filter, and how does it work?
A space-efficient probabilistic structure to test set membership with possible false positives. It uses multiple hash functions to set/check bits in a bit array.
6. What is a Fibonacci heap?
A heap data structure with better amortized operations, using a collection of trees, supporting decrease-key in O(1) amortized time.
7. How do you merge two sorted linked lists?
Iterate both lists, compare heads, append the smaller to a new list, and continue until all nodes are merged.
8. What is the difference between a binary heap and a binomial heap?
Binary heap: a single tree structure. Binomial heap: a collection of binomial trees that allow faster merge operations.
9. How do you implement a hash map from scratch?
Use an array of buckets, a hash function to map keys to indices, and collision resolution (chaining or open addressing) for key-value storage.
10. What is the difference between a red-black tree and an AVL tree?
Both are self-balancing trees. AVL trees are more strictly balanced, offering faster lookups but slower inserts/deletes. Red-black trees are more relaxed, yielding faster modifications.
Algorithms
1. How does counting sort work?
It counts occurrences of each value in the input, then calculates positions based on cumulative counts, producing a sorted output in linear time given a limited range.
2. What is the difference between a stable and an unstable sorting algorithm?
Stable sorts preserve the relative order of equal elements; unstable sorts may not.
3. Explain the traveling salesman problem.
A NP-hard problem asking for the shortest route that visits each city exactly once and returns to the origin, optimizing travel cost.
4. How does the Knuth-Morris-Pratt algorithm work for string searching?
KMP preprocesses the pattern to create a prefix table, then uses it to skip re-examining characters on mismatches, achieving efficient search.
5. What is the Rabin-Karp algorithm?
A string search algorithm using hashing to find any set of pattern strings in a text, efficiently checking potential matches via hash comparisons.
6. How do you calculate the power of a number without using the pow function?
Use exponentiation by squaring: recursively square base and reduce exponent, handling even/odd exponents.
7. How do you find the least common multiple (LCM) of two numbers?
Compute LCM(a, b) = |a * b| / GCD(a, b), using the greatest common divisor.
8. What is the Bellman-Ford algorithm?
An algorithm to find shortest paths from a single source in a weighted graph, handling negative weights, relaxing edges repeatedly.
9. How do you generate permutations of a string?
Recursively swap characters and generate permutations for remaining substring, backtracking after each recursion.
10. Explain the concept of amortized time complexity.
Average time per operation over a sequence, smoothing out costly operations with cheaper ones to guarantee overall efficiency.
Web Development
1. What is a single-page application (SPA)?
A web app that loads a single HTML page and dynamically updates content without full page reloads, offering a smoother user experience.
2. How do you optimize images for web performance?
Compress images, use appropriate formats, resize to needed dimensions, lazy-load, and use responsive images.
3. What is a service worker?
A script running in the background of a browser, enabling offline capabilities, caching, and background sync.
4. How does lazy loading work in web applications?
Defers loading of non-critical resources (images, scripts) until needed, improving initial load time and performance.
5. What is the difference between async and defer in script tags?
async downloads the script asynchronously and executes immediately when ready. defer downloads asynchronously but executes after HTML parsing.
6. How does browser caching work?
Stores resources locally based on HTTP headers, reducing network requests for subsequent visits.
7. What is the difference between a relative and an absolute URL?
Relative URLs specify a path relative to the current location; absolute URLs include the full path including protocol and domain.
8. What are webhooks, and how are they used?
Webhooks are HTTP callbacks triggered by events, allowing one application to notify another in real-time.
9. Explain the difference between a session and a token-based authentication.
Sessions store user state on the server with session IDs, while token-based authentication uses stateless tokens (e.g., JWT) exchanged with each request.
10. How do you prevent clickjacking?
Use X-Frame-Options or Content Security Policy headers to prevent your pages from being framed by other sites.
Security
1. What is a replay attack, and how do you prevent it?
A replay attack intercepts and resends valid data transmissions. Prevent with nonces, timestamps, or sequence numbers to ensure uniqueness.
2. What are salted hashes, and why are they important?
Salting adds random data to passwords before hashing, preventing attackers from using precomputed tables to reverse hashes.
3. How do you ensure secure data transmission over HTTP?
Use HTTPS/TLS to encrypt data in transit, validating certificates and using strong cipher suites.
4. What is the principle of least privilege?
Granting only the minimum necessary permissions to users or processes, reducing risk if compromised.
5. How does two-factor authentication (2FA) work?
Requires two forms of verification (e.g., password plus OTP) to improve account security.
6. What is the difference between symmetric and asymmetric encryption?
Symmetric uses the same key for encryption/decryption; asymmetric uses a public-private key pair for secure communication.
7. How do you secure a REST API?
Use HTTPS, authenticate/authorize requests (OAuth, JWT), validate inputs, rate-limit, and sanitize data.
8. What is a buffer overflow?
A vulnerability where a program writes more data to a buffer than it can hold, potentially overwriting adjacent memory.
9. Explain the concept of a honeypot in cybersecurity.
A decoy system set up to attract attackers, gathering intelligence while diverting them from real assets.
10. What is DNS poisoning?
An attack that corrupts DNS records, redirecting traffic to malicious sites.
Databases
1. What is a surrogate key in databases?
A system-generated unique identifier for a record, not derived from application data.
2. How do you implement a full-text search in a database?
Use database-specific features (like SQL Server Full-Text Search, PostgreSQL tsvector) or external indexing engines (Elasticsearch) to index and search text.
3. What is database indexing, and what are its drawbacks?
Indexing creates a data structure to speed up queries. Drawbacks include increased storage, slower writes, and maintenance overhead.
4. Explain eventual consistency in distributed databases.
A consistency model where updates propagate gradually, so that all nodes will converge to the same state given time.
5. What is a composite key?
A key composed of multiple columns that uniquely identify a record.
6. How does a bitmap index work?
Uses bitmaps for each distinct value in a column, mapping row presence. Efficient for read-heavy, low-cardinality data.
7. What are the differences between OLTP and OLAP?
OLTP handles transactional processing with many short operations. OLAP supports analytical queries on large datasets with complex operations.
8. What is a materialized view?
A precomputed, stored query result that can be refreshed, speeding up read operations.
9. How do you perform a database rollback?
Use transaction control (e.g., ROLLBACK) to undo changes within a transaction if an error occurs.
10. What is the difference between normalization and denormalization?
Normalization reduces redundancy by splitting data. Denormalization combines data for performance, increasing redundancy.
System Design
1. How do you design a notification system?
Design a scalable publisher-subscriber model with message queues, user preferences, delivery channels (email, SMS, push), and real-time updates.
2. What is a distributed cache, and how does it work?
A cache spread across multiple machines, storing frequently accessed data for fast retrieval and reducing load on databases.
3. How do you design a high-availability database system?
Use replication, clustering, failover mechanisms, data partitioning, and backup strategies to ensure minimal downtime.
4. What is a circuit breaker pattern?
A design that stops making requests to a failing service, allowing it time to recover, and preventing cascading failures.
5. How do you manage configuration in large-scale systems?
Centralized configuration services, environment variables, configuration files, and dynamic updates with versioning.
6. What is the purpose of an API rate limiter?
To restrict the number of requests a client can make in a time period, preventing abuse and ensuring fair resource usage.
7. How do you design a recommendation engine?
Collect user data, use collaborative/filtering algorithms or machine learning models, scale with data processing pipelines, and personalize suggestions.
8. What is sharding, and how does it differ from partitioning?
Sharding splits a database horizontally across servers. Partitioning divides data logically, which may occur on a single server or across systems.
9. How would you handle write-heavy systems?
Optimize for concurrency, use write-optimized databases, queue writes, scale horizontally, employ caching, and batch operations.
10. How do you design a chat system?
Use real-time messaging protocols (WebSockets), message queues, user presence indicators, scalable storage for history, and ensure low latency.
Advanced Programming Topics
1. What is speculative execution in CPUs?
CPUs predict future instructions and execute them ahead of time, increasing performance but potentially causing security issues like Spectre.
2. How does garbage collection work in Java?
Java’s GC periodically identifies unreachable objects and frees memory, using algorithms like mark-and-sweep or generational collection.
3. What is a coroutine, and how is it different from a thread?
Coroutines are lightweight, cooperative units of execution that yield control explicitly, whereas threads are managed by the OS and preemptively scheduled.
4. What are memory barriers, and why are they used?
Memory barriers enforce ordering of memory operations, critical in multi-threaded programming to prevent unexpected behavior due to reordering.
5. How does dependency resolution work in package managers?
It analyzes required packages, their versions, and dependencies, resolving conflicts to install a consistent set of packages.
6. What is the difference between transactional and eventual consistency?
Transactional consistency provides immediate, atomic consistency. Eventual consistency guarantees that, over time, all nodes converge to the same state.
7. What is the purpose of zero-copy in networking?
Zero-copy techniques avoid extra data copying between buffers to improve performance and reduce CPU usage during data transfer.
8. What is a software interrupt?
A programmatic interrupt triggered by software instructions to invoke OS services, differing from hardware interrupts triggered by devices.
9. Explain the actor model in distributed systems.
A concurrency model where independent “actors” communicate via message passing, encapsulating state and behavior to avoid shared state issues.
10. How do you implement an LRU (Least Recently Used) cache?
Use a combination of a hash map for fast lookups and a doubly linked list to track recency. On access, move item to front; on insertion, remove least recently used from tail if capacity exceeded.