# Software Engineer
**Role:** Software Engineer · **Level:** L4
**Company:** [Jane Street](https://scaleengineer.com/companies/jane-street)
**Difficulty:** Hard
**Salary:** US$120000 - US$180000
**Experience:** 3 - 7
**Timeline:** ~14 days
The Software Engineer L4 interview at Jane Street is a rigorous process designed to assess a candidate's technical proficiency, problem-solving abilities, and cultural fit within the firm. It typically involves multiple rounds, including technical interviews focusing on data structures, algorithms, and system design, as well as behavioral interviews to gauge teamwork and communication skills. The goal is to identify candidates who can contribute effectively to complex trading systems and thrive in a fast-paced, collaborative environment.
Canonical: https://scaleengineer.com/interviews/jane-street/l4-software-engineer
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## Overall evaluation

- Technical Proficiency
- Analytical and Creative Thinking
- Teamwork and Cultural Fit

## Questions asked

- Given an array of integers, find the contiguous subarray with the largest sum.
- Design a system to store and retrieve user profiles for a social media platform.
- Implement a function to reverse a linked list.
- How would you detect a cycle in a directed graph?
- Explain the difference between a process and a thread.
- Describe a time you disagreed with a teammate and how you resolved it.
- What are the trade-offs between using a relational database and a NoSQL database?
- Write a function to find the k-th smallest element in an unsorted array.
- How would you design a rate limiter for an API?
- Tell me about a challenging project you worked on and your role in it.

## Preparation tips

### lists

- Master core data structures and algorithms: Focus on arrays, linked lists, trees, graphs, hash tables, heaps, and sorting/searching algorithms.
- Practice coding problems: Utilize platforms like LeetCode, HackerRank, and AlgoExpert, focusing on medium to hard difficulty problems.
- Study system design: Understand concepts like scalability, availability, consistency, load balancing, caching, and database design.
- Review operating systems and computer architecture: Understand processes, threads, memory management, and I/O.
- Brush up on probability and statistics: Basic understanding can be helpful for certain roles.
- Prepare for behavioral questions: Reflect on past experiences related to teamwork, problem-solving, and handling challenges.
- Understand Jane Street's business: Research the company's focus on quantitative trading and market making.
- Practice mock interviews: Simulate the interview environment to get comfortable with the pressure and format.

### studyPlan

- {"title":"Data Structures Fundamentals","longDescription":"Weeks 1-2: Focus on fundamental data structures (arrays, linked lists, stacks, queues, hash maps) and basic algorithms (sorting, searching). Practice implementing these from scratch and analyze their time and space complexity. Solve easy to medium problems on these topics.","shortDescription":"Weeks 1-2: Data Structures & Basic Algorithms. Practice easy/medium problems."}
- {"title":"Advanced Data Structures and Algorithms","longDescription":"Weeks 3-4: Dive into more advanced data structures like trees (binary trees, BSTs, AVL trees, tries) and graphs (traversals, shortest path algorithms). Work on medium to hard problems involving these structures.","shortDescription":"Weeks 3-4: Advanced Data Structures (Trees, Graphs) & Algorithms. Practice medium/hard problems."}
- {"title":"System Design","longDescription":"Weeks 5-6: Focus on system design principles. Study concepts like API design, database choices (SQL vs. NoSQL), caching strategies, load balancing, message queues, and microservices. Practice designing common systems like Twitter feed, URL shortener, etc.","shortDescription":"Weeks 5-6: System Design Principles. Practice designing common systems."}
- {"title":"Core CS Concepts and Behavioral Preparation","longDescription":"Weeks 7-8: Review operating systems concepts (processes, threads, concurrency, memory management) and computer architecture basics. Also, dedicate time to behavioral preparation, thinking about STAR method examples for common questions.","shortDescription":"Weeks 7-8: OS Concepts, Computer Architecture & Behavioral Prep. Prepare STAR examples."}
- {"title":"Intensive Practice and Mock Interviews","longDescription":"Weeks 9-10: Intensive practice of mixed problems covering all topics. Focus on timed mock interviews to simulate the actual interview conditions. Refine coding style and communication during explanations.","shortDescription":"Weeks 9-10: Mixed Problem Practice & Mock Interviews. Focus on speed and communication."}

## Location differences

- {"location":"New York","differences":{"tips":["Familiarize yourself with common trading system architectures.","Practice explaining complex technical concepts clearly and concisely.","Be prepared to discuss your experience with high-performance computing.","Research Jane Street's specific areas of focus in quantitative trading.","Highlight any experience with C++, Python, or other relevant languages in a financial context."],"interviewFocus":["System design for low-latency trading platforms","Concurrency and multithreading in financial systems","Performance optimization of trading algorithms","Understanding of financial markets and instruments (basic)","Adaptability to new technologies and market changes"],"commonQuestions":["Discuss a time you had to debug a complex system under pressure.","How would you design a system to handle real-time stock price updates for a large number of users?","Explain the trade-offs between different database technologies for a high-frequency trading application.","Describe a challenging technical problem you solved and your approach.","How do you stay updated with the latest technologies in quantitative finance?"]}}
- {"location":"London","differences":{"tips":["Review common distributed systems patterns and trade-offs.","Be ready to whiteboard solutions to algorithmic problems.","Emphasize your ability to work in a team and communicate technical ideas effectively.","Showcase your understanding of software development best practices.","Prepare examples of how you've contributed to the success of a project."],"interviewFocus":["Distributed systems design and implementation","Data structures and algorithms with a focus on efficiency","Understanding of operating systems and network protocols","Problem-solving under time constraints","Collaboration and communication with non-technical stakeholders"],"commonQuestions":["How would you design a distributed system for risk management in a trading firm?","Explain the concept of garbage collection and its impact on performance in a trading environment.","Describe a situation where you had to collaborate with traders or quantitative researchers.","What are the challenges of building scalable financial data pipelines?","How do you approach testing and ensuring the reliability of critical financial software?"]}}
- {"location":"Hong Kong","differences":{"tips":["Understand the lifecycle of financial data and common processing challenges.","Be prepared to discuss security best practices relevant to financial systems.","Practice explaining your thought process for performance optimization.","Consider how functional programming concepts might apply to trading systems.","Highlight your ability to learn and adapt to new technologies and methodologies."],"interviewFocus":["Data analysis and processing at scale","Software security principles","Performance tuning and optimization techniques","Experience with functional programming paradigms","Adaptability and learning agility"],"commonQuestions":["Design a system for processing and analyzing large volumes of market data.","How do you ensure the security of financial applications?","Discuss your experience with performance profiling and optimization.","What are your thoughts on functional programming in the context of financial modeling?","Describe a time you had to adapt your technical approach based on feedback."]}}

## Round 1: Technical Coding Round 1
**Type:** Data Structures and Algorithms Interview · **Difficulty:** Medium · **Duration:** 45 min
Solve 1-2 coding problems, focusing on data structures and algorithms.
This round focuses on your fundamental data structures and algorithms knowledge. You will be asked to solve one or two coding problems on a whiteboard or shared editor. The interviewer will assess your ability to understand the problem, devise an efficient solution, and implement it correctly. They will also evaluate your communication skills as you explain your thought process.
**Interviewers look for:** Ability to translate a problem into a working algorithm.; Understanding of time and space complexity.; Clean and readable code.; Ability to communicate the solution effectively.
**Evaluation criteria:** Correctness of the solution.; Efficiency of the solution (time and space complexity).; Clarity and quality of the code.; Problem-solving approach and thought process.
**Common rejection reasons:** Inability to articulate thought process clearly.; Poorly structured or inefficient code.; Lack of understanding of fundamental data structures and algorithms.; Failure to consider edge cases or constraints.
## Questions

- Given a binary tree, determine if it is a valid binary search tree.
- Find the length of the longest substring without repeating characters.

## Preparation tips

- Practice coding on a whiteboard or in a plain text editor.
- Be prepared to discuss the time and space complexity of your solutions.
- Think out loud and explain your approach before you start coding.
- Ask clarifying questions if the problem statement is unclear.

## Round 2: System Design Round
**Type:** System Design Interview · **Difficulty:** Hard · **Duration:** 60 min
Design a scalable system, discussing trade-offs and components.
This round assesses your ability to design large-scale, distributed systems. You'll be given an open-ended problem, such as designing a URL shortener or a social media feed. The interviewer will expect you to discuss requirements, propose a high-level design, dive into specific components, and consider aspects like scalability, availability, and data storage.
**Interviewers look for:** Ability to design complex systems from scratch.; Understanding of distributed systems concepts.; Knowledge of various technologies and their applications.; Ability to think about edge cases and potential bottlenecks.
**Evaluation criteria:** Scalability of the proposed design.; Reliability and fault tolerance.; Clarity and completeness of the design.; Understanding of trade-offs and justifications for design choices.; Ability to handle ambiguity and make reasonable assumptions.
**Common rejection reasons:** Inability to design a scalable and robust system.; Overlooking critical components or failure points.; Lack of understanding of trade-offs in system design.; Poor communication of design choices.
## Questions

- Design a system like TinyURL.
- Design a distributed cache.

## Preparation tips

- Study common system design patterns and architectures.
- Practice designing systems like Twitter, Facebook news feed, etc.
- Be prepared to discuss trade-offs between different design choices.
- Think about potential bottlenecks and how to address them.
- Clearly articulate your design and justify your decisions.

## Round 3: Behavioral and Managerial Round
**Type:** Behavioral Interview · **Difficulty:** Medium · **Duration:** 45 min
Discuss past experiences, teamwork, and motivation using the STAR method.
This round focuses on your past experiences, motivations, and how you handle various workplace situations. You'll be asked behavioral questions using the STAR method (Situation, Task, Action, Result). The interviewer wants to understand your strengths, weaknesses, how you collaborate, and your overall fit with the team and company culture.
**Interviewers look for:** Evidence of problem-solving skills in real-world scenarios.; Ability to work effectively in a team.; Proactiveness and ownership.; Cultural alignment with Jane Street's collaborative and intellectually curious environment.
**Evaluation criteria:** Past experiences and accomplishments.; Behavioral competencies (teamwork, problem-solving, leadership).; Communication and interpersonal skills.; Motivation and alignment with company values.
**Common rejection reasons:** Lack of relevant experience or inability to provide specific examples.; Poor communication or inability to articulate past experiences.; Apparent lack of interest or motivation.; Poor cultural fit or inability to work collaboratively.
## Questions

- Tell me about a time you faced a significant technical challenge and how you overcame it.
- Describe a situation where you had to work with a difficult colleague. How did you handle it?
- Why are you interested in working at Jane Street?

## Preparation tips

- Prepare specific examples using the STAR method for common behavioral questions.
- Be ready to discuss your resume in detail.
- Think about your career goals and why you are interested in Jane Street.
- Ask thoughtful questions about the team, culture, and role.

## Round 4: Final Technical Round
**Type:** Advanced Technical Interview · **Difficulty:** Hard · **Duration:** 60 min
Tackle complex algorithmic problems and advanced CS concepts.
This is often a final technical round, potentially involving more complex algorithmic problems or a deeper dive into specific technical areas relevant to the role. It might also include a mix of coding and conceptual questions to thoroughly assess your technical depth and problem-solving capabilities.
**Interviewers look for:** Exceptional problem-solving abilities.; Creativity in finding solutions.; Robustness and efficiency of code.; Ability to think critically and adapt.
**Evaluation criteria:** Advanced problem-solving skills.; Deep understanding of algorithms and data structures.; Ability to handle complex and ambiguous problems.; Performance on challenging coding tasks.
**Common rejection reasons:** Inability to solve complex algorithmic problems under pressure.; Fundamental misunderstandings in advanced CS concepts.; Poor performance across multiple technical rounds.; Lack of enthusiasm or engagement.
## Questions

- Given a set of intervals, merge all overlapping intervals.
- Implement a function to find the median of a data stream.

## Preparation tips

- Revisit advanced algorithms like dynamic programming, graph algorithms, and greedy algorithms.
- Practice problems that require creative thinking and optimization.
- Be prepared for questions that might combine multiple concepts.
- Stay calm and methodical when faced with difficult problems.