Criteo

Principal Software Engineer

Software EngineerL7Hard

The Principal Software Engineer (L7) interview at Criteo is a rigorous process designed to assess deep technical expertise, leadership potential, and strategic thinking. Candidates are expected to demonstrate a strong command of software engineering principles, experience in designing and scaling complex systems, and the ability to mentor and guide other engineers. The interview process typically involves multiple rounds, including technical deep dives, system design, behavioral assessments, and a final discussion with senior leadership.

Rounds

4

Timeline

~14 days

Experience

8 - 15 yrs

Salary Range

US$170000 - US$220000

Total Duration

225 min

Overall Evaluation Criteria

Technical Proficiency

Technical depth and breadth
Problem-solving skills
System design and architecture
Scalability and performance considerations
Leadership and mentorship
Communication and collaboration
Cultural fit and alignment with Criteo's values

Leadership and Impact

Ability to lead technical projects
Mentoring and guiding junior engineers
Driving technical innovation
Strategic thinking and long-term vision

Behavioral and Cultural Fit

Behavioral examples demonstrating problem-solving
Handling of challenging situations
Teamwork and collaboration skills
Adaptability and learning agility

Preparation Tips

1Deeply understand Criteo's business, products, and technology stack.
2Review fundamental computer science concepts (data structures, algorithms, operating systems, networking).
3Practice system design problems, focusing on scalability, reliability, and trade-offs.
4Prepare specific examples from your past experience that demonstrate leadership, problem-solving, and impact.
5Familiarize yourself with common ad-tech concepts and challenges.
6Practice articulating your thought process clearly and concisely.
7Research the interviewers on LinkedIn to understand their backgrounds.

Study Plan

1

Data Structures & Algorithms

Weeks 1-2: DSA fundamentals. LeetCode (Medium/Hard).

Weeks 1-2: Focus on core data structures and algorithms. Review common patterns and complexity analysis. Practice problems on platforms like LeetCode (Medium/Hard).

2

System Design

Weeks 3-4: System Design. Distributed systems, databases, caching.

Weeks 3-4: Dive into system design principles. Study topics like distributed systems, databases, caching, load balancing, and message queues. Read system design case studies.

3

Behavioral Preparation

Week 5: Behavioral preparation. STAR method.

Week 5: Prepare for behavioral questions using the STAR method (Situation, Task, Action, Result). Reflect on your career experiences, focusing on leadership, challenges, and successes.

4

Company and Domain Research

Week 6: Criteo research. Ad-tech domain.

Week 6: Research Criteo's ad-tech domain, recent news, and technical challenges. Understand the ad ecosystem and Criteo's role within it. Prepare questions for the interviewers.

Commonly Asked Questions

Design a distributed caching system for a high-traffic website.
How would you optimize the performance of a slow-running API?
Describe a time you had to influence a team's technical direction.
What are the trade-offs between SQL and NoSQL databases for a specific use case?
How do you approach mentoring junior engineers?
Tell me about a complex technical problem you solved.
How would you design a system to detect fraudulent ad clicks?
What are your thoughts on microservices vs. monolith architectures?
Describe your experience with cloud platforms like AWS, Azure, or GCP.
How do you handle technical debt?
What is your approach to code reviews?
How do you stay up-to-date with new technologies?

Location-Based Differences

Paris

Interview Focus

Emphasis on distributed systems design and scalability.Assessment of leadership and mentorship capabilities.Evaluation of strategic thinking and long-term technical vision.

Common Questions

How would you design a real-time bidding system for online advertising?

Discuss a time you had to make a significant technical trade-off. What was the outcome?

How do you approach performance optimization in a large-scale distributed system?

Describe your experience with cloud-native architectures (e.g., Kubernetes, microservices).

Tips

Be prepared to discuss your contributions to open-source projects.
Highlight experience with high-traffic, low-latency systems.
Showcase your ability to influence technical direction and mentor junior engineers.

New York

Interview Focus

Focus on problem-solving and analytical skills.Assessment of collaboration and communication within a team.Evaluation of adaptability to new technologies and methodologies.

Common Questions

Design a system to handle millions of concurrent users for a social media platform.

Tell me about a time you led a team through a challenging technical project.

How do you ensure the reliability and fault tolerance of a distributed system?

What are your thoughts on the future of AI in ad-tech?

Tips

Prepare examples demonstrating your ability to break down complex problems.
Emphasize your experience in agile development environments.
Be ready to discuss your understanding of Criteo's business and the ad-tech landscape.

London

Interview Focus

Emphasis on data-driven decision making and impact.Assessment of technical depth in specific domains (e.g., machine learning, data engineering).Evaluation of ability to drive technical initiatives from conception to delivery.

Common Questions

How would you design a recommendation engine for an e-commerce platform?

Describe a situation where you had to deal with a major production incident. How did you resolve it?

What are the key considerations when designing for massive data volumes?

Discuss your experience with A/B testing and experimentation frameworks.

Tips

Quantify your achievements with data and metrics.
Be prepared to discuss your contributions to system architecture and design.
Showcase your ability to mentor and grow engineering talent.

Process Timeline

1
Data Structures and Algorithms60m
2
System Design and Architecture60m
3
Behavioral and Leadership Assessment45m
4
Executive and Strategic Alignment60m

Interview Rounds

4-step process with detailed breakdown for each round

1

Data Structures and Algorithms

Assess core coding skills and problem-solving using data structures and algorithms.

Technical Coding InterviewHard
60 minSenior Software Engineer / Staff Engineer

This round focuses on your core programming skills and problem-solving abilities. You will be given one or two coding problems, typically involving data structures and algorithms. The interviewer will assess your ability to understand the problem, devise an efficient solution, write clean and correct code, and analyze its time and space complexity. Expect to discuss trade-offs and edge cases.

What Interviewers Look For

Strong coding skills.Ability to translate requirements into working code.Understanding of fundamental data structures and algorithms.Clean and maintainable code.

Evaluation Criteria

Correctness of code
Efficiency of algorithms
Code quality and readability
Problem-solving approach
Understanding of time and space complexity

Questions Asked

Given a binary tree, find the lowest common ancestor of two given nodes.

TreeRecursionBinary Tree

Implement a function to find the k-th largest element in an unsorted array.

ArraySortingHeap

Design a data structure that supports insert, delete, search, and getRandom in O(1) average time.

Hash TableArrayRandomization

Preparation Tips

1Practice coding problems on platforms like LeetCode, HackerRank, or Coderbyte.
2Focus on common data structures (arrays, linked lists, trees, graphs, hash maps) and algorithms (sorting, searching, dynamic programming, graph traversal).
3Practice explaining your thought process out loud as you code.
4Be prepared to discuss edge cases and optimize your solution.

Common Reasons for Rejection

Lack of fundamental CS knowledge.
Inability to articulate solutions clearly.
Poor performance on coding challenges.
Not meeting the bar for algorithmic thinking.
2

System Design and Architecture

Assess ability to design scalable and reliable distributed systems.

System Design InterviewHard
60 minStaff Engineer / Principal Engineer

This round evaluates your ability to design and architect large-scale distributed systems. You'll be presented with a high-level problem (e.g., design Twitter's feed, design a URL shortener) and expected to break it down, identify components, define APIs, and discuss scalability, reliability, and trade-offs. Focus on clarifying requirements, making reasonable assumptions, and justifying your design choices.

What Interviewers Look For

Ability to design complex, scalable, and reliable systems.Deep understanding of distributed systems principles.Proficiency in choosing appropriate technologies and justifying decisions.Consideration of non-functional requirements (scalability, availability, latency, consistency).

Evaluation Criteria

System design approach
Scalability and performance
Reliability and fault tolerance
Choice of technologies and justifications
Understanding of trade-offs
Handling of edge cases and failure scenarios

Questions Asked

Design a system to count unique visitors to a website in real-time.

System DesignScalabilityData Processing

Design a distributed rate limiter.

System DesignDistributed SystemsConcurrency

How would you design a notification system for millions of users?

System DesignScalabilityMessaging

Preparation Tips

1Study common system design patterns and architectures.
2Understand concepts like load balancing, caching, databases (SQL vs. NoSQL), message queues, CDNs, and microservices.
3Practice designing systems for scale, considering factors like read/write patterns, data partitioning, and consistency models.
4Be prepared to discuss trade-offs between different design choices.
5Review case studies of large-scale systems.

Common Reasons for Rejection

Inability to design scalable and reliable systems.
Lack of consideration for trade-offs.
Poor understanding of distributed systems concepts.
Not addressing non-functional requirements adequately.
3

Behavioral and Leadership Assessment

Assess leadership, teamwork, and cultural fit through behavioral questions.

Behavioral And Managerial InterviewMedium
45 minHiring Manager / Engineering Manager

This round focuses on your past experiences, leadership potential, and how you work within a team. You'll be asked behavioral questions designed to elicit specific examples of your accomplishments, challenges faced, and how you handled them. Prepare to discuss your career goals, motivations, and why you're interested in Criteo and this specific role.

What Interviewers Look For

Evidence of leadership and initiative.Ability to work effectively in a team.Strong communication skills.Alignment with Criteo's culture and values.Passion for technology and the company's mission.

Evaluation Criteria

Leadership qualities
Teamwork and collaboration
Problem-solving approach in past projects
Communication skills
Cultural fit
Motivation and career aspirations

Questions Asked

Tell me about a time you had to lead a project from start to finish.

LeadershipProject ManagementBehavioral

Describe a situation where you disagreed with a teammate or manager. How did you handle it?

Conflict ResolutionTeamworkCommunication

How do you prioritize your work when faced with multiple competing tasks?

Time ManagementPrioritizationBehavioral

Preparation Tips

1Prepare specific examples using the STAR method (Situation, Task, Action, Result) for common behavioral questions.
2Think about situations where you demonstrated leadership, teamwork, conflict resolution, and problem-solving.
3Research Criteo's company culture and values.
4Be ready to articulate your strengths and weaknesses.
5Prepare thoughtful questions to ask the interviewer about the team, role, and company.

Common Reasons for Rejection

Lack of leadership experience.
Poor communication or collaboration skills.
Inability to provide specific examples of impact.
Not demonstrating alignment with Criteo's values.
4

Executive and Strategic Alignment

Discuss strategic thinking, technical vision, and leadership with senior management.

Senior Leadership / Executive InterviewHard
60 minDirector of Engineering / VP of Engineering

This final round is typically with a senior leader (Director or VP). It's a broader discussion about your career, your technical philosophy, your leadership style, and your vision for the future. They will assess your strategic thinking, your ability to influence at a high level, and your potential to contribute to Criteo's long-term technical success. Be prepared to discuss your biggest technical achievements and challenges.

What Interviewers Look For

A clear technical vision and strategy.The ability to influence technical direction across teams.Understanding of how technology drives business value.Experience mentoring and developing other engineers.Strong communication and presentation skills.

Evaluation Criteria

Strategic thinking
Technical vision
Business acumen
Influence and impact
Mentorship capabilities
Communication with senior leadership

Questions Asked

What is your vision for the future of ad-tech engineering?

VisionStrategyAd-Tech

Describe a time you had to make a significant technical decision with incomplete information.

Decision MakingRisk ManagementBehavioral

How would you foster innovation within an engineering team?

LeadershipInnovationTeam Management

Preparation Tips

1Think about your long-term career goals and how this role aligns with them.
2Prepare to discuss your technical philosophy and approach to engineering leadership.
3Consider how you would contribute to Criteo's technical strategy.
4Be ready to discuss your experience mentoring and growing engineering teams.
5Have thoughtful questions prepared about the company's direction and challenges.

Common Reasons for Rejection

Lack of strategic vision.
Inability to connect technical decisions to business impact.
Poor communication with senior stakeholders.
Not demonstrating the gravitas expected of a Principal Engineer.

Commonly Asked DSA Questions

Frequently asked coding questions at Criteo

View all
Two SumEASYValid ParenthesesEASYSearch in Rotated Sorted ArrayMEDIUMMerge Sorted ArrayEASYIntersection of Two ArraysEASYRansom NoteEASYRandom Pick with WeightMEDIUMFlood FillEASY