# Senior Software Engineer
**Role:** Software Engineer · **Level:** L4
**Company:** [Criteo](https://scaleengineer.com/companies/criteo)
**Difficulty:** Medium to Hard
**Salary:** US$110000 - US$150000
**Experience:** 4 - 10
**Timeline:** ~14 days
The Senior Software Engineer (L4) interview process at Criteo is designed to assess a candidate's technical expertise, problem-solving abilities, system design skills, and cultural fit. It typically involves multiple rounds, including technical interviews, a system design interview, and a behavioral/managerial interview. The process aims to identify individuals who can contribute significantly to complex projects, mentor junior engineers, and uphold Criteo's engineering standards.
Canonical: https://scaleengineer.com/interviews/criteo/l4-software-engineer
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## Overall evaluation

- Technical Skills
- System Design
- Behavioral and Leadership

## Questions asked

- Describe a time you had to deal with a difficult stakeholder. How did you handle it?
- How would you design a system to handle real-time bidding in advertising?
- What are the trade-offs between monolithic and microservices architectures?
- Write a function to find the k-th largest element in an unsorted array.
- Explain the concept of eventual consistency.
- Tell me about a project you are particularly proud of and your role in it.
- How do you approach debugging a complex distributed system?
- Design an API for a simple e-commerce product catalog.
- What strategies do you use to ensure code quality and maintainability?
- How do you stay updated with new technologies and industry trends?

## Preparation tips

### lists

- Review fundamental computer science concepts (data structures, algorithms, operating systems, databases).
- Practice coding problems regularly, focusing on efficiency and clarity.
- Study system design principles and common architectural patterns.
- Prepare specific examples from your past experience to answer behavioral questions using the STAR method (Situation, Task, Action, Result).
- Research Criteo's products, services, and company culture.
- Understand the technologies commonly used at Criteo (e.g., Java, Python, Scala, distributed systems, cloud platforms).
- Prepare thoughtful questions to ask the interviewer about the role, team, and company.

### studyPlan

- {"title":"Data Structures and Algorithms Fundamentals","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 efficiently and analyze their time/space complexity. Solve LeetCode problems tagged 'Medium'.","shortDescription":"Weeks 1-2: Data Structures & Algorithms (Medium LeetCode)."}
- {"title":"System Design","longDescription":"Weeks 3-4: Deep dive into system design concepts. Study topics like load balancing, caching, database scaling (sharding, replication), message queues, microservices architecture, and API design. Review common system design interview questions and practice designing systems like Twitter feed, URL shortener, etc.","shortDescription":"Weeks 3-4: System Design Principles & Practice."}
- {"title":"Behavioral and Cultural Fit","longDescription":"Week 5: Prepare for behavioral questions. Reflect on your past projects and experiences, identifying examples that showcase leadership, teamwork, problem-solving, and conflict resolution. Structure these using the STAR method. Research Criteo's values and prepare to articulate how you align with them.","shortDescription":"Week 5: Behavioral Preparation (STAR Method) & Company Research."}
- {"title":"Final Preparation","longDescription":"Week 6: Mock interviews, focusing on both technical and behavioral aspects. Refine your explanations and practice articulating your thought process clearly. Review any weak areas identified during practice.","shortDescription":"Week 6: Mock Interviews & Final Review."}

## Location differences

- {"location":"Paris","differences":{"tips":["Familiarize yourself with Criteo's core business and technologies.","Practice coding problems on platforms like LeetCode, focusing on medium to hard difficulty.","Prepare detailed examples for behavioral questions using the STAR method.","Research common system design patterns and be ready to discuss trade-offs."],"interviewFocus":["Strong emphasis on practical problem-solving and coding proficiency.","System design questions often relate to Criteo's ad-tech domain.","Behavioral questions focus on collaboration and impact within a team."],"commonQuestions":["How would you design a URL shortener service?","Discuss a challenging technical problem you solved recently.","Explain the trade-offs between SQL and NoSQL databases.","How do you handle concurrency in your applications?","Describe your experience with cloud platforms (AWS, GCP, Azure)."]}}
- {"location":"New York","differences":{"tips":["Deep dive into distributed systems concepts and algorithms.","Be prepared to whiteboard complex system designs.","Highlight experiences with large-scale data processing and real-time systems.","Understand Criteo's global presence and how that impacts engineering decisions."],"interviewFocus":["Greater emphasis on distributed systems and scalability.","System design questions may be more abstract and theoretical.","Behavioral questions might explore leadership potential and cross-functional collaboration."],"commonQuestions":["Design a distributed caching system.","How would you scale a social media feed?","Explain the CAP theorem and its implications.","What are the principles of RESTful API design?","Describe your experience with microservices architecture."]}}

## Round 1: Coding and Algorithms Round
**Type:** Technical Phone Screen / Online Assessment · **Difficulty:** Medium · **Duration:** 45 min
Coding problems focusing on data structures and algorithms.
This initial technical round focuses on assessing your core programming skills and problem-solving abilities. You will be asked to solve one or two coding problems, typically involving data structures and algorithms. The interviewer will evaluate how you approach the problem, your thought process, the efficiency of your solution, and the clarity of your code. Expect to write code in a shared editor or on a whiteboard.
**Interviewers look for:** Logical thinking; Ability to translate requirements into code; Understanding of fundamental CS concepts; Clean and efficient coding style
**Evaluation criteria:** Problem-solving approach; Correctness of the solution; Code efficiency (time and space complexity); Code readability and maintainability; Communication of thought process
**Common rejection reasons:** Inability to articulate thought process clearly.; Poor coding practices (e.g., inefficient code, lack of error handling).; Fundamental misunderstanding of data structures or algorithms.; Difficulty in solving even basic coding problems.
## Questions

- Given a binary tree, invert the tree.
- Find the first non-repeating character in a string.
- Implement a function to check if a linked list has a cycle.

## Preparation tips

- Practice coding problems on platforms like LeetCode, HackerRank, or Coderbyte.
- Focus on understanding the time and space complexity of your solutions.
- Be prepared to explain your approach before you start coding.
- Practice thinking out loud as you solve problems.

## Round 2: System Design Round
**Type:** System Design Interview · **Difficulty:** Hard · **Duration:** 60 min
Design a scalable and reliable system for an open-ended problem.
This round assesses your ability to design complex, scalable, and reliable systems. You'll be given an open-ended problem (e.g., design a service like Twitter, a URL shortener, or a notification system) and expected to discuss various aspects, including data modeling, API design, component interactions, scalability strategies, and potential bottlenecks. The focus is on your thought process, trade-off analysis, and ability to handle ambiguity.
**Interviewers look for:** Architectural thinking; Experience with large-scale systems; Ability to break down complex problems; Knowledge of various system components (databases, caches, queues); Pragmatic approach to design
**Evaluation criteria:** Ability to design scalable and reliable systems; Understanding of distributed systems concepts; Consideration of trade-offs; Clarity of design and communication; Handling of edge cases and failure scenarios
**Common rejection reasons:** Lack of depth in system design knowledge.; Inability to handle ambiguity in requirements.; Poor consideration of trade-offs (scalability, reliability, cost).; Not asking clarifying questions.; Focusing too much on implementation details too early.
## Questions

- Design a distributed key-value store.
- Design a rate limiter for an API.
- Design a system to count unique visitors to a website in real-time.

## Preparation tips

- Study common system design patterns and architectures.
- Practice designing systems for scale and reliability.
- Be prepared to discuss trade-offs between different approaches.
- Think about data storage, caching, load balancing, and fault tolerance.
- Ask clarifying questions to define the scope and requirements.

## Round 3: Behavioral and Team Fit Round
**Type:** Behavioral / Managerial Interview · **Difficulty:** Medium · **Duration:** 45 min
Assesses teamwork, communication, and cultural fit through behavioral questions.
This round focuses on your behavioral competencies, teamwork abilities, and overall fit with Criteo's culture. You'll be asked questions about your past experiences, how you handle challenges, work with others, and your career aspirations. The interviewer aims to understand your working style, your ability to collaborate, and how you might contribute to the team and company.
**Interviewers look for:** Team player attitude; Communication clarity; Ownership and accountability; Growth mindset; Cultural alignment
**Evaluation criteria:** Collaboration and teamwork skills; Problem-solving approach in team settings; Leadership potential; Adaptability and learning agility; Alignment with Criteo's culture and values
**Common rejection reasons:** Lack of self-awareness.; Inability to provide specific examples.; Poor communication or interpersonal skills.; Mismatch with team culture or company values.; Lack of enthusiasm or engagement.
## Questions

- Tell me about a time you disagreed with a teammate. How did you resolve it?
- Describe a situation where you had to learn a new technology quickly.
- How do you prioritize your work when you have multiple competing deadlines?

## Preparation tips

- Prepare specific examples using the STAR method for common behavioral questions.
- Reflect on your strengths and weaknesses.
- Think about your motivations for joining Criteo.
- Be ready to discuss your career goals and how this role fits into them.
- Show enthusiasm and genuine interest in the company and the role.