# Principal SDE
**Role:** Software Engineer · **Level:** N
**Company:** [Expedia](https://scaleengineer.com/companies/expedia)
**Difficulty:** Very High
**Salary:** US$180000 - US$250000
**Experience:** 10 - 15
**Timeline:** ~4 days
Expedia is looking for a Principal Software Engineer to join our dynamic team. This role is critical in driving technical strategy, mentoring junior engineers, and delivering high-impact solutions. We are seeking experienced individuals with a proven track record of technical leadership and innovation.
Canonical: https://scaleengineer.com/interviews/expedia/n-software-engineer
---
## Overall evaluation

- Technical Proficiency
- System Design & Architecture
- Leadership & Mentorship
- Communication & Collaboration
- Cultural Fit

## Questions asked

- Describe a complex system you designed or significantly contributed to. What were the key challenges and how did you address them?
- How would you design a system to handle millions of concurrent users for a travel booking website?
- Tell me about a time you had to lead a team through a difficult technical challenge.
- What are your thoughts on the future of travel technology?
- How do you stay updated with the latest technology trends?
- Explain the trade-offs between different database technologies for a large-scale application.
- Describe a situation where you disagreed with a technical decision made by your team or manager. How did you handle it?
- How would you mentor a junior engineer who is struggling with a particular concept?
- What are the key principles of building a scalable and resilient microservices architecture?
- How do you approach performance optimization in a distributed system?

## Preparation tips

### lists

- Thoroughly review your resume and be prepared to discuss every project in detail.
- Brush up on core computer science fundamentals, including data structures and algorithms.
- Practice system design problems, focusing on scalability, reliability, and trade-offs.
- Prepare examples of leadership, mentorship, and problem-solving from your past experience.
- Research Expedia's products, services, and recent news.
- Understand Expedia's company culture and values.
- Prepare thoughtful questions to ask the interviewers.

### studyPlan

- {"title":"Foundational Computer Science","longDescription":"Weeks 1-2: Focus on core data structures (arrays, linked lists, trees, graphs, hash tables) and algorithms (sorting, searching, dynamic programming, graph traversal). Practice implementing these in your preferred language and analyze their time and space complexity. Review object-oriented design principles and common design patterns.","shortDescription":"Weeks 1-2: Data Structures, Algorithms, OOP, Design Patterns."}
- {"title":"System Design & Architecture","longDescription":"Weeks 3-4: Deep dive into system design concepts. Study distributed systems, databases (SQL vs. NoSQL), caching strategies, message queues, load balancing, and microservices architecture. Practice designing common systems like URL shorteners, social media feeds, or e-commerce platforms.","shortDescription":"Weeks 3-4: System Design, Distributed Systems, Databases, Caching, Microservices."}
- {"title":"Behavioral & Leadership","longDescription":"Weeks 5-6: Prepare for behavioral questions using the STAR method (Situation, Task, Action, Result). Reflect on your leadership experiences, conflict resolution, project management, and instances where you demonstrated initiative or mentorship. Research Expedia's values and prepare examples that align with them.","shortDescription":"Weeks 5-6: Behavioral Questions (STAR method), Leadership, Mentorship, Expedia Values."}
- {"title":"Technology & Project Deep Dive","longDescription":"Week 7: Focus on specific technologies relevant to Expedia (e.g., cloud platforms like AWS, specific programming languages, big data technologies). Review your past projects and identify key technical challenges and solutions. Prepare to discuss your contributions and impact.","shortDescription":"Week 7: Technology Deep Dive, Project Review, Cloud Platforms."}
- {"title":"Mock Interviews & Final Preparation","longDescription":"Week 8: Mock interviews with peers or mentors. Practice articulating your thoughts clearly and concisely, especially during system design discussions. Refine your answers to common behavioral questions and prepare insightful questions for the interviewers.","shortDescription":"Week 8: Mock Interviews, Communication Practice, Final Review."}

## Location differences

- {"location":"Seattle, USA","differences":{"tips":["Be prepared to discuss your most challenging technical projects in detail.","Highlight instances where you influenced technical direction or mentored teams.","Showcase your understanding of system design principles and trade-offs.","Emphasize your experience with large-scale, high-traffic systems.","Be ready to articulate your vision for future technology trends."],"interviewFocus":["Deep understanding of distributed systems and scalability.","Proven ability to lead complex technical projects.","Strong architectural design skills.","Mentorship and team leadership capabilities.","Experience with cloud platforms (AWS, Azure, GCP)."],"commonQuestions":["How would you design a distributed caching system for a global e-commerce platform?","Describe a time you had to make a significant technical trade-off. What was the situation and your decision-making process?","How do you approach mentoring and developing junior engineers?","Discuss your experience with cloud-native architectures and microservices.","What are your strategies for ensuring code quality and maintainability in large-scale systems?"]}}
- {"location":"London, UK","differences":{"tips":["Prepare examples of how you've improved system performance or reliability.","Be ready to discuss your approach to managing technical debt.","Highlight your experience in leading cross-functional teams.","Showcase your ability to think strategically about technology roadmaps.","Demonstrate your understanding of data-driven decision-making."],"interviewFocus":["Expertise in data engineering and real-time analytics.","Ability to handle complex operational challenges.","Strong leadership and strategic thinking.","Experience in optimizing system performance.","Understanding of agile methodologies and their application at scale."],"commonQuestions":["How would you design a real-time data processing pipeline for travel recommendations?","Tell me about a time you had to resolve a major production issue under pressure.","What are your strategies for fostering a culture of innovation within an engineering team?","Discuss your experience with performance optimization in large-scale applications.","How do you balance technical debt with the need for rapid feature delivery?"]}}
- {"location":"Singapore","differences":{"tips":["Be prepared to discuss your experience with API design patterns.","Provide examples of how you've successfully advocated for technical changes.","Emphasize your understanding of security principles.","Showcase your ability to design for failure and resilience.","Highlight your experience with automation and continuous delivery."],"interviewFocus":["Deep knowledge of API design and management.","Strong communication and influencing skills.","Expertise in security best practices.","Experience in building highly available systems.","Proficiency in modern DevOps and CI/CD practices."],"commonQuestions":["Design a scalable API gateway for a global travel booking platform.","Describe a situation where you had to influence stakeholders to adopt a new technology.","How do you ensure the security and compliance of software systems?","What is your approach to building resilient and fault-tolerant systems?","Discuss your experience with CI/CD pipelines and DevOps practices."]}}

## Round 1: HR/Recruiter Screen
**Type:** Recruiter Screen · **Difficulty:** High · **Duration:** 60 min
Initial screening to assess basic qualifications and cultural fit.
This initial screening call with a recruiter is designed to assess your overall fit for the role and Expedia. They will discuss your background, career aspirations, and motivation for applying. It's also an opportunity for you to learn more about the company culture and the specifics of the position. Be prepared to talk about your resume highlights and why you are interested in this Principal SDE role.
**Interviewers look for:** Clear and concise communication.; Ability to break down complex problems.; Logical thinking and problem-solving approach.
**Evaluation criteria:** Technical communication skills.; Ability to articulate thought process.; Understanding of fundamental computer science concepts.
**Common rejection reasons:** Lack of clarity in explaining technical concepts.; Inability to articulate system design trade-offs.; Insufficient experience in leading technical projects.; Poor communication or collaboration skills.; Not demonstrating a proactive or problem-solving attitude.
## Questions

- Tell me about yourself and your career journey.
- Why are you interested in Expedia and this specific role?
- What are your salary expectations?
- What are your strengths and weaknesses?
- Can you describe your experience with [specific technology mentioned in job description]?

## Preparation tips

- Review your resume and be ready to summarize your experience.
- Research Expedia's mission, values, and recent news.
- Prepare questions about the role, team, and company culture.
- Be enthusiastic and professional.

## Round 2: System Design
**Type:** System Design Interview · **Difficulty:** Very High · **Duration:** 60 min
Assesses your ability to design scalable and robust systems.
This round focuses on your ability to design complex, scalable, and reliable systems. You will be presented with a high-level problem statement (e.g., design a ride-sharing service, a news feed, or a distributed cache) and expected to walk through your design process, including data modeling, API design, component interactions, and scalability considerations. Be prepared to discuss trade-offs and justify your decisions.
**Interviewers look for:** Structured approach to problem-solving.; Deep understanding of distributed systems.; Ability to articulate design choices and trade-offs.; Consideration of non-functional requirements (scalability, availability, etc.).
**Evaluation criteria:** System design capabilities.; Understanding of scalability, reliability, and performance.; Ability to handle ambiguity and make design decisions.; Knowledge of various architectural patterns and technologies.
**Common rejection reasons:** Inability to design a scalable and robust system.; Poor understanding of distributed systems concepts.; Difficulty in identifying and discussing trade-offs.; Lack of depth in explaining technical choices.; Failure to consider edge cases or failure scenarios.
## Questions

- Design a URL shortening service like bit.ly.
- Design a system to count unique visitors to a website in real-time.
- How would you design a distributed rate limiter?
- Design a notification service for a large-scale application.
- Design a system to store and retrieve user profiles for millions of users.

## Preparation tips

- Practice system design problems extensively.
- Familiarize yourself with common system design patterns.
- Think about scalability, availability, consistency, and latency.
- Be ready to draw diagrams and explain your design clearly.
- Consider different technologies and their pros/cons for specific use cases.

## Round 3: Coding & Algorithms
**Type:** Technical Coding Interview · **Difficulty:** Very High · **Duration:** 60 min
Assesses coding skills and knowledge of data structures and algorithms.
This round involves solving one or two coding problems, typically focusing on data structures and algorithms. You'll be expected to write code in a shared editor, explain your thought process, discuss time and space complexity, and handle edge cases. The problems will be challenging and require a deep understanding of CS fundamentals.
**Interviewers look for:** Correctness and efficiency of the solution.; Clean and well-structured code.; Ability to explain the solution and its complexity.; Good debugging skills.
**Evaluation criteria:** Proficiency in coding.; Understanding of data structures and algorithms.; Ability to write clean, efficient, and maintainable code.; Problem-solving skills through coding.
**Common rejection reasons:** Incorrect or inefficient solutions to coding problems.; Inability to explain code logic or complexity.; Difficulty in debugging code.; Lack of understanding of fundamental algorithms and data structures.; Poorly written or unoptimized code.
## Questions

- Given a binary tree, find the lowest common ancestor of two given nodes.
- Implement a function to find the k-th largest element in an unsorted array.
- Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
- Find the length of the longest substring without repeating characters.
- Implement a Least Recently Used (LRU) cache.

## Preparation tips

- Practice coding problems on platforms like LeetCode, HackerRank, etc.
- Focus on medium to hard difficulty problems.
- Master common data structures and algorithms.
- Practice explaining your code and complexity analysis.
- Be comfortable coding in your preferred language.

## Round 4: Managerial/Leadership Interview
**Type:** Behavioral & Leadership Interview · **Difficulty:** High · **Duration:** 60 min
Evaluates leadership, mentorship, and strategic thinking.
This interview focuses on your leadership, mentorship, and strategic thinking. You'll be asked behavioral questions about your past experiences, focusing on how you've led teams, mentored engineers, resolved conflicts, and influenced technical direction. The interviewer will also assess your understanding of the Principal SDE role and your vision for contributing to Expedia's technical growth.
**Interviewers look for:** Evidence of technical leadership.; Ability to mentor and grow engineers.; Experience in driving technical strategy.; Strong communication and interpersonal skills.; Alignment with Expedia's values.
**Evaluation criteria:** Leadership and mentorship capabilities.; Problem-solving and decision-making skills.; Communication and influencing abilities.; Strategic thinking and technical vision.; Cultural alignment.
**Common rejection reasons:** Lack of leadership or mentorship experience.; Inability to articulate past technical decisions and their impact.; Poor handling of conflict or challenging situations.; Not demonstrating strategic thinking.; Failure to align with company values or culture.
## Questions

- Describe a time you mentored a junior engineer. What was the outcome?
- Tell me about a significant technical challenge you faced and how you led your team to overcome it.
- How do you handle disagreements within a technical team?
- What is your approach to technical debt management?
- How would you define success for a Principal Engineer at Expedia?

## Preparation tips

- Prepare specific examples using the STAR method for leadership, mentorship, conflict resolution, and strategic decision-making.
- Think about your leadership philosophy and how you foster team growth.
- Be ready to discuss your technical vision and how it aligns with Expedia's goals.
- Research Expedia's engineering culture and values.

## Round 5: Senior Leadership Interview
**Type:** Executive/Senior Leadership Interview · **Difficulty:** Very High · **Duration:** 45 min
Final discussion with senior leadership on strategy and vision.
This final interview is typically with a senior leader (Director or VP) to assess your strategic thinking, leadership potential, and overall fit for a Principal role. They will likely ask high-level questions about technology trends, your vision for the team or domain, and how you would contribute to Expedia's long-term success. This is your chance to demonstrate your executive presence and strategic impact.
**Interviewers look for:** High-level technical strategy.; Business acumen.; Strong communication and influencing skills.; Vision for the future of technology at Expedia.
**Evaluation criteria:** Strategic thinking and technical vision.; Ability to influence and communicate with senior leadership.; Understanding of business goals and technology's role.; Overall fit for a Principal level role.
**Common rejection reasons:** Lack of alignment with senior leadership's vision.; Inability to articulate strategic technical direction.; Poor communication with senior stakeholders.; Not demonstrating a deep understanding of the business impact of technology.; Failure to inspire confidence at a senior level.
## Questions

- What are the biggest technological challenges facing the travel industry today?
- How would you drive technical innovation within your team and across the organization?
- Describe a time you had to influence senior leadership on a technical decision.
- What is your long-term vision for the technology stack in your area?
- How do you measure the success of a technical initiative?

## Preparation tips

- Understand Expedia's business strategy and how technology supports it.
- Formulate your vision for technical innovation and leadership.
- Be prepared to discuss high-level architectural concepts and industry trends.
- Practice articulating your impact and value proposition at a senior level.