Imagine walking into a technical interview and feeling completely confident, knowing you’re about to tackle any question thrown your way. That’s the power of preparation — and we’re here to make sure you’re ready for anything.

We asked 50 developers in our community who recently landed jobs to share the toughest technical interview questions they faced, and here’s what they said.

The Purpose and Structure of Technical Interviews

Technical interviews are a crucial part of the hiring process for software engineering and technical roles. They allow companies to thoroughly evaluate your technical skills, problem-solving abilities, and soft skills necessary to succeed in the role.

Technical interview formats can vary, but they commonly involve a combination of coding challenges, system design questions, and behavioral interview questions.

Overall, technical interview questions are designed to thoroughly evaluate your technical and soft skills. Understanding and preparing for each interview component will help you master your next technical interview.

💡 Struggling with interview prep? Book a 1:1 session with our technical interview experts from Amazon, Microsoft, and Google to sharpen your skills. Your first 15 minutes are free!

Coding and Programming Questions

Coding challenges test your ability to solve problems with code, while programming questions analyze your programming abilities. Coding challenges typically involve writing code to accomplish a certain task, optimizing existing code, discussing approaches to theoretical coding problems, or a combination of these.

The technical interview questions may range from simple syntax and logic challenges to more complex algorithm and data structure problems. Here are some typical categories of coding interview questions:

Data Structures

The interviewer may ask you questions about fundamental data structures like arrays, linked lists, stacks, queues, trees, graphs, and hash tables. Be ready to implement basic operations like traversal, search, insertion, and deletion. Knowledge of the time and space complexities needed for key data structure operations will also help.

Algorithms

Algorithm questions test your problem-solving skills. Study up on sorting or divide-and-conquer algorithms — quicksort, merge sort, heap sort, etc. — and efficient searching techniques like binary search. Be prepared for algorithm design questions asking you to build an algorithm from scratch.

Time and Space Complexity

Brush up on Big O notation. The interviewer may ask you to analyze algorithm complexity for time and space and indicate the most efficient data structures and algorithms.

Language-Specific Concepts

The interviewer may ask you coding questions tailored to languages like Java, Python, C++, JavaScript, etc. Review language-specific syntax, classes, data structures, and concepts, as well as how key features like inheritance, polymorphism, lambdas, and closures work. Be ready to demonstrate language proficiency.

Design Patterns

You may also be asked basic questions regarding key software design patterns. Brush up on:

• SOLID design principles
• Creational patterns — singleton, factory, builder, etc.
• Structural patterns — MVC, facade, etc.
• Behavioral patterns — observer strategy, etc.

Common Coding and Programming Questions

• What coding language are you most comfortable with?

  • Sample Answer: “While I am comfortable with several coding languages including SQL, Python, C++, and Visual Basic, the one I have the most hands-on experience working with is JavaScript. JavaScript was the first coding language I learned, and I have used it on several projects over the past 10 years.”

• What is a SAN, and how is it used?

  • Sample Answer: “A SAN, or Storage Area Network, is a high-speed, specialized network that provides block-level network access to storage. It can be used to improve application availability, enhance performance, increase storage utilization and effectiveness, and improve data security and protection.”

• When is it appropriate to denormalize database design?

  • Sample Answer: “Denormalization is a database optimization technique used to improve a database’s performance for specific queries. You may need denormalization to make improvements to a database so that it meets your application requirements. However, denormalization can impact what your database can do, so it’s important to make sure that you need denormalization for scalability or performance before choosing to use it as an optimization technique.”

• What are continuous integration systems, and what is their role in the automated-build process?

  • Sample Answer: “Continuous integration is a developmental process, which requires developers to integrate code into a shared repository several times throughout the day. Each time the code is integrated, it’s verified by the automated build. This allows for early detection of defects and problems within the codebase.”

With practice on real interview coding problems, you can master the coding skills needed to tackle the common programming questions that come up in technical interviews. Try reviewing coding problems on platforms like LeetCode and HackerRank to continue improving.

System Design Principles

Many technical interviews, especially for software engineering roles, will test your knowledge of object-oriented programming (OOP) and system design principles. The OOP and system design questions will assess your ability to design solutions for real-world software systems and leverage key OOP concepts to architect large, scalable applications.

The interviewer will present a technical problem and comprehensively evaluate your approach to the system design process, with considerations like tradeoffs, bottlenecks, and scalability. The interviewer may ask you to design components or APIs for real-world products and services.

For example, you could be asked to design a news feed, payment system, or ridesharing app. This task will test how you identify the core objects, attributes, and behaviors within a system. Make sure you employ proper data encapsulation and use techniques like inheritance and polymorphism.

To ace system design questions, clarify requirements first. Then, start with a high-level design, identifying the core components and interactions. Drill down into specifics on request, like writing out class definitions, APIs, or schema.

Verbalize your thought process as you work through the problem. Ask clarifying questions, state your assumptions, and explain the rationale for your choices. Discuss tradeoffs associated with different design decisions.

Showcase your expertise in topics like:

• Design patterns — factory, singleton, MVC, observer, etc.
• Database structure and normalization
• APIs and microservices
• Scaling and performance optimization
• Multithreading and concurrency
• Caching strategies
• Networking and communication protocols

Common OOP and System Design Questions

• Design an e-commerce site, and indicate the classes and methods you would need.

  • Sample Answer: “To design an e-commerce site, I would start with classes like User, Product, Cart, Order, and Payment. The User class would handle user authentication and profile management, while the Product class would manage product details and inventory. The Cart class would handle items added by the user, the Order class would process and store order details, and the Payment class would manage payment processing and confirmation. The methods would include addToCart(), removeFromCart(), checkout(), processPayment(), and trackOrder()”

• Design a parking garage system, and detail how you would structure the classes and relationships.

  • Sample Answer: “For a parking garage system, I would design classes such as ParkingGarage, ParkingSpot, Vehicle, and Ticket. The ParkingGarage class would manage the overall structure, including a list of ParkingSpots — with each ParkingSpot having attributes like spotID, level, and availability. The Vehicle class would have attributes like licensePlate and vehicleType, while the Ticket class would track the entry and exit times and associated fees. The methods would include parkVehicle(), findAvailableSpot(), issueTicket(), and calculateFee().”

• Implement an ATM software system. Specify the classes, attributes, and behaviors you would need.

  • Sample Answer: “For an ATM software system, the primary classes would be ATM, Account, Card, Transaction, and Bank. The ATM class would manage user interactions and hardware control, while the Account class would store account details and balance. The Card class would link to the Account and handle authentication, whereas the Transaction class would handle different transaction types like withdrawal, deposit, and balance inquiry. The methods would include authenticateUser(), selectTransaction(), dispenseCash(), and printReceipt(), while the attributes would comprise accountNumber, balance, transactionID, and cardNumber.”

With practice, system design interviews get much easier. Mastering OOP principles will prepare you to analyze and model real-world systems in an interview setting.

💡 Struggling with interview prep? Book a 1:1 session with our technical interview experts from Amazon, Microsoft, and Google to sharpen your skills. Your first 15 minutes are free!

Database and SQL Queries

Databases are crucial to most software systems, so it’s highly likely that your technical interview questions will test your knowledge about database design, SQL queries, optimization, and scaling. Be prepared to discuss topics like:

Schema Design and Normalization

• Designing an efficient database schema, which avoids data redundancy and anomalies
• Describing normalization concepts like 1NF, 2NF, and 3NF
• Deciding when to denormalize a database schema to optimize for read performance

SQL Commands and Queries

• Writing basic CRUD (create, read, update, delete) statements with SQL
• Joining multiple tables together in complex SQL queries
• Aggregating functions and grouping, sorting, and filtering data with SQL

Query Optimization and Performance

• Using techniques like adding indexes and partitioning to improve query performance
• Analyzing query execution plans to identify and fix bottlenecks
• Balancing normalization and denormalization to optimize for your use cases

NoSQL Databases and Horizontal Scaling

• Listing reasons for using NoSQL databases like MongoDB, Cassandra, etc.
• Partitioning data across shards to scale databases horizontally
• Explaining tradeoffs between NoSQL systems and traditional SQL databases

Overall, be ready to write actual SQL statements and queries during the interview. Having a solid grasp of relational databases and experience with SQL is essential for most backend and full-stack roles.

Front-End and Back-End Web Development

Front-end and back-end development requires different but complementary skill sets. Here are some of the key technical aspects you may need to brush up on:

Front-End

• HTML/CSS: Prepare to answer questions regarding your experience with HTML5, CSS3, responsive design, cross-browser compatibility, accessibility, etc. You may also be asked to discuss projects showcasing your HTML/CSS skills.
• JavaScript: Expect questions testing your JavaScript proficiency, including language features like closures, prototypes, callbacks, promises, and asynchronous programming.
• React: Prepare to answer questions related to React architecture, component design, state management with Redux, common hooks (e.g., useState/useEffect), performance optimization, etc. You may also be asked to discuss your previous React projects.
• Angular: Angular interview questions may cover components, directives, services, dependency injection, change detection, routing, pipes, forms, etc. Prepare to highlight your experience with Angular framework best practices.

Back-End

• Node.js: Demonstrate your Node.js skills by discussing event-driven programming, asynchronous I/O, module exports, npm, Express web framework, REST APIs, database integration, performance, etc.
• PHP: Expect PHP interview questions on language fundamentals (e.g., variables, arrays, loops, and functions), MySQL integration, and MVC frameworks (e.g., Laravel, REST APIs, security, sessions, cookies, and caching).
• Ruby/Rails: You may need to showcase your experience with object-oriented Ruby, Rails MVC framework, ActiveRecord ORM, REST APIs, authentication, asset pipeline, caching strategies, background jobs, etc.
• Python/Django: Be ready to discuss Python basics (e.g., data structures, OOP, decorators, and exception handling), Django MVT architecture, ORM, template engine, admin interface, caching, security, etc.
• Java/Spring: Prepare for Java interview questions on data structures, multithreading, collections, JVM, Spring framework, dependency injection, REST APIs, database access, performance tuning, etc.
• API Design: Expect questions on REST API design principles, authentication/authorization, versioning, documentation, rate limiting, caching, microservices, GraphQL, gRPC, OpenAPI specification, etc.

To succeed in this kind of interview, highlight full-stack projects that demonstrate your expertise in front-end, back-end, APIs, databases, security, scalability, and performance.

DevOps and Software Engineering Principles

DevOps and software engineering best practices are critical topics in technical interviews. The interviewer will assess your expertise in continuous integration/continuous deployment (CI/CD) pipelines and infrastructure as code (IaC), as well as in monitoring, and writing clean, maintainable code. Here’s the information you’ll be expected to have:

CI/CD Pipelines

Be prepared to discuss your experience with CI/CD pipelines and automation. Key areas you may highlight include:

• Experience setting up build pipelines and release workflows in tools, like Jenkins, CircleCI, TravisCI, and GitHub Actions
• Knowledge of automating builds, tests, and deployments
• Troubleshooting and optimizing pipelines for faster feedback
• Implementing pipeline stages like build, test, analysis, staging, and production
• Leveraging containers and orchestration with Kubernetes and Docker

IaC

IaC is a critical DevOps practice. Be ready to discuss:

• Writing IaC with tools like Terraform, CloudFormation, Ansible, and Puppet
• Benefits like consistency, reproducibility, and version control
• Immutable and mutable infrastructure patterns
• Infrastructure testing and validation techniques

Monitoring and Observability

The interviewer may ask you about your experience with:

• Monitoring tools like Prometheus, Grafana, and ELK stack
• Logging strategies and analyzing logs with Kibana
• Tracing distributed systems with Jaeger
• Dashboards and alerts for proactive monitoring

Design Patterns

Just like coding and programming interviews, DevOps and software engineering interviews may include questions on software design patterns. Be prepared to demonstrate your knowledge of SOLID design principles, as well as creational, structural, and behavioral patterns.

Writing Maintainable Code

The interviewer may ask you to:

• Write modular, reusable code with a separation of concerns
• Perform unit testing and test-driven development techniques
• Refactor code, and improve legacy codebases
• Use static code analysis tools, linting, and code formatting
• Apply agile development practices and continuous improvement

💡 Struggling with interview prep? Book a 1:1 session with our technical interview experts from Amazon, Microsoft, and Google to sharpen your skills. Your first 15 minutes are free!

Behavioral and Situational Questions

Technical roles require strong communication, teamwork, creativity, and problem-solving, which can be assessed through open-ended behavioral questions. Therefore, behavioral and situational questions are an important part of technical interviews. With these questions, your interviewer can evaluate your soft skills and cultural fit.

You’ll be provided hypothetical scenarios to gauge your leadership, teamwork, and communication skills, as well as your ability to apply technical knowledge to real-world problems.

Common Behavioral and Situational Questions

When answering behavioral questions, be specific and use real examples from your work experiences. Use the STAR method when answering:

• Explain the Situation you encountered
• Elaborate the Task at hand
• Indicated the Actions you took
• State the Results you achieved

Here are some common behavioral questions and answers:

• What was your role and specific responsibilities on the most recent project you worked on?

• Sample Answer: “On my most recent project, I was the lead backend developer for a fintech application. My responsibilities included designing and implementing RESTful APIs, optimizing database queries, and ensuring the security of financial transactions. I also coordinated with front-end developers to integrate user-facing features and conducted code reviews to maintain code quality.”

• What is the project you are most proud of, and how did you contribute to it?

• Sample Answer: “I am the most proud of a machine learning project where we developed a recommendation engine for an e-commerce platform. I specifically worked on designing the data pipeline, selecting appropriate algorithms, and fine-tuning models for accuracy. The project resulted in a 15% increase in user engagement and a significant boost in sales.”

• Do you prefer to work alone or on a team?

• Sample Answer: “I enjoy both. When I work alone, I can focus on complex problems, while with team collaboration, I appreciate learning diverse perspectives and ideas, which enhance creativity and innovation. In my current role, I can consistently strike an effective balance between solo tasks and team projects and meetings.”

• What would you do if you were asked to perform a task but weren’t sure how to complete it?

• Sample Answer: “If I were unsure about how to complete a task, I would first try to understand the requirements and research possible solutions. If needed, I wouldn’t hesitate to ask for guidance from my colleagues or seek clarification from my manager. In this way, I’ll be able to learn and complete the tasks accurately while maintaining productivity.”

• Tell me about a time you went above and beyond your expected tasks while working on a project.

• Sample Answer: “While working on a deadline-driven project, I noticed a potential performance bottleneck in our codebase. Despite it not being part of my assigned tasks, I took the initiative to refactor the code and optimize database queries. That improved the system’s performance by 20% and helped us meet the project deadline with a more robust solution.”

• How would you overcome the challenge of working with a difficult coworker on a team project?

• Sample Answer: “I would first try to understand the coworker’s perspective and identify the root cause of the conflict. I believe in open communication and would have a candid conversation to address any issues. Finding common ground and aligning our goals would help us collaborate effectively. If necessary, I would also seek mediation from a manager to make sure that the work environment remains positive.”

For situational questions, the interviewer will describe a hypothetical scenario and ask how you’d handle it.

• Your team is rushing to meet a deadline, and tension is high, but a junior developer makes a mistake that sets the project back. How would you address this situation?

• Sample Answer: “I would first have a candid conversation with the junior developer and find out what exactly went wrong. Based on their clarification, I would try to find a solution. I may even ask the team for help if we are really short on time. In the worst-case scenario, I would check with our manager if a deadline extension is possible. After the project is completed, I would discuss ways to avoid such mistakes in the future with the junior developer.”

• You believe your engineering team is relying on outdated technologies and processes. How would you convince management that it’s time to upgrade?

• Sample Answer: “I would first make sure I have complete information about the up-to-date technologies and processes available to us. Only then, I would talk to the management about the possible solutions — explaining the pros and cons of each solution and clarifying the shortcomings of the technologies and processes we are using currently. If there are budgetary issues, I would try to find more affordable options.”

Behavioral and situational questions allow you to showcase soft skills critical for technical roles. Use them as opportunities to prove that you can apply your technical expertise in real-world environments.

Technical Project Discussion

In this section, you’ll need to demonstrate hands-on experience and collaboration skills. The interviewer may ask you to walk them through a major technical project or accomplishment from your background.

Here are the things you should consider when discussing technical projects:

• Provide an overview of the project’s purpose and your role: what business or technical challenge did it aim to address, and how did you contribute?
• Explain the key technical decisions and problem-solving involved. Discuss your thought process, and weigh the tradeoffs you considered.
• Highlight how you collaborated with cross-functional teams, such as product managers, designers, or other engineers. Interviewers want to see that you can work well with a diverse set of stakeholders.
• Focus on your responsibilities and technical accomplishments. Don’t just state your role, but emphasize your unique contributions and quantifiable results as well.
• Illustrate your work with specific examples and anecdotes. Zoom in on a coding challenge or milestone moment to bring the project to life.
• Explain the technologies you used and the architectural decisions you made. It’s fine to say you don’t remember every detail.
• If you can, try to relate the project to the role you’re interviewing for. Demonstrate how you leveraged relevant technical skills.
• Conclude by summarizing your key takeaways and learning outcomes from the project experience. Elaborate on what you learned about the technology and working in collaboration.

Technical project discussions are where you can shine! With preparation and practice, you’ll be able to confidently walk through your technical projects and highlight the specialized skills you need for the role.

Tips for Acing the Interview

To ace the technical interview, practice regularly with sample code and design questions. Websites like LeetCode have an extensive database of questions to practice with. Treat each practice interview like the real deal — explain your thought process thoroughly and, at every step, verbalize your approach, assumptions, and logic.

Get comfortable asking clarifying questions when you don’t fully understand a problem. It’s perfectly acceptable to ask for additional details or restate the problem in your own words. These initiatives show that you deeply comprehend each task before attempting to solve it.

Admit if you get stuck or hit a dead end — don’t try to fudge your way through technical interview questions you aren’t equipped to answer. Ask follow-up questions to keep the discussion going. To fully explore the problem space, quiz the interviewer about edge cases and test scenarios.

Technical interviews are a two-way street, so make sure you are assessing whether the role is a good fit for you as well. With practice and preparation, you’ll be ready to tackle whatever tough technical questions come your way.

Following Up After the Interview

After you’ve showcased your knowledge and skills, it’s time for possibly one of the most important steps: following up. It will determine the final impression you leave on your interviewer.

Here are some best practices for following up:

• Briefly recap two or three key qualifications and strengths that make you a great fit for the role to remind the interviewer of what you bring to the table.
• Express your enthusiasm for the role and the company and state that you’re very interested in the opportunity based on what you learned during the interview.
• Reiterate your passion for the company’s work and mission and align your values and motivation with its goals.
• To exemplify reflection and accountability, briefly address any points you could’ve expanded on or questions you felt you could’ve answered better.
• Provide your contact information again. Be ready to provide any additional information and be available for follow-up discussions.
• End on a gracious, professional note: thank the interviewer again, and state that you look forward to hearing back from them.

With a proper follow-up after a technical interview, you can strengthen your candidacy and set you apart from other applicants. A thoughtful thank you message can reinforce why you are the ideal choice for the role.

💡 Struggling with interview prep? Book a 1:1 session with our technical interview experts from Amazon, Microsoft, and Google to sharpen your skills. Your first 15 minutes are free!

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• Source: https://www.codementor.io/blog/technical-interview-questions-jqbigasqsn