Jane Street Is a New York-based quantitative trading firm with more than 2,600 employees worldwide as of 2025 and offices in New York, London, Hong Kong, Singapore and Amsterdam. The requirements for Jane Street SWE are very different from most technology companies: no financial background is required, no OCaml experience is required, but you are required to have a strong ability to build systems from scratch, and a mind that can reason clearly under pressure.
STAGE 01── Recruiter Call
The recruiter call takes approximately 30 minutes and is a standard process:
- Brief background introduction
- Ask why you are interested in Jane Street
- Understanding of the position
Important lessons: Don’t reveal your expected salary in this round, and don’t mention your interview progress at other companies. These are important bargaining chips for subsequent negotiations, and it is not cost-effective to deal with them in advance.
Recruiter will tell you "the SWE interview asks practical coding questions, not LeetCode questions". This sentence is true, but it is also easily misleading - it does not mean that the topic is simple, but that the examination method is different and closer to the real engineering scenario.
Language selection suggestions: Jane Street uses OCaml extensively internally, but officials have made it clear not to use OCaml just to please the interviewer. Just use the language you are most familiar with and can perform best. In fact, most engineers hired come on board with no functional programming experience.
STAGE 02── Technical Phone Screen 1 (60 minutes)
Topic:Expression evaluation with variables(Similar to the enhanced version of the LC 772 Basic Calculator II)
Question description: Given a string expression, supporting + – * /, brackets and variables (variable values are given through dictionaries), calculate the value of the expression. The expression may contain spaces.
Example: expression = “(x + y) * 2 – z”, variables = {“x”: 5, “y”: 3, “z”: 4} → output 12
Solution process:
- I first implemented the basic version with two stacks (numeric stack + operator stack), handling multiplication and division precedence and parentheses.
- Interviewer Follow-up: Added variable support.
- Follow-up: Supports rounding down for negative numbers and division.
- I modified the code in real time and finally completed a more complete solution.
The interviewer focused on how I handle priorities and edge cases (such as dividing by 0, empty strings, etc.).
STAGE 03──Technical Phone Screen 2 (60 minutes)
Topic:Design a text editor that supports undo/redo
Solution process:
- I'll use it firstTwo Stacks(history stack + redo stack) implements basic undo/redo functions.
- The interviewer added additional requirements: Support batch undo (undo multiple steps at one time) and text selection replacement.
- I introduced Command Pattern, encapsulating each operation into an object, successfully supporting expansion requirements.
- Finally, we discussed how to optimize if the amount of text is large (mentioning the Rope data structure).
This round focuses on examining abstraction capabilities and code scalability.
Super Day (4–5 rounds throughout the day)
Round 1 (AM): Practical Coding – Building from Scratch
Topic: Implement the core state class of the Connect Four game. It is required to support moves, determine victory or defeat, detect draws, and handle illegal operations.
Solution process:
- I use a two-dimensional array to represent the chessboard and maintain the height of each column for quick placement.
- Four victory judgments are realized: horizontal, vertical, forward oblique, and reverse oblique.
- Interviewer Follow-up: Add the regret function. I quickly modified the code to support undo.
Round 2 (AM): Recursion and Abstraction
Topic: Implement a function wrapper with Memoization that requires only one expensive calculation for the same input, and then directly returns the cached result.
Solution process:
- I use decorator + dictionary to implement memoization.
- Follow-up: supports functions with parameters + cache size limit (LRU style).
- I implemented the final version using functools.lru_cache combined with a manual dictionary.
Round 3 (PM): System Design Deep Dive
Topic: Design a real-time bidding system (similar to a simplified version of eBay bidding system) that needs to support high concurrent bidding, real-time result broadcast, and consistency guarantee.
Solution process:
- I first drew the overall architecture (Load Balancer + Auction Service + Notification Service).
- Discussed the optimistic locking vs. Message queue trade-off.
- Follow-up: How to deal with a sudden 10-fold increase in concurrency? I proposed a sharding + current limiting solution.
Round 4 (PM): In-depth project report + behavioral interview
Let me walk you through a high-performance logging system project on my resume, asking a lot of design decisions and technical trade-offs. Finally, I asked about the team’s experience in handling disagreements.
Write at the end
During the preparation process for this Jane Street interview, I deeply felt the importance of "thinking from scratch" and "expressing clearly". Simply answering questions is no longer enough, you must improve your engineering intuition and communication skills under unfamiliar problems.
If you are also preparing for an interview with Jane Street or other top companies and feel that your preparation direction is not clear enough and efficient, you can find out. Programhelp, focusing on providing OA practical assistance And practical guidance on interviewing. We will provide targeted help such as high-frequency question sorting, mock interviews, code iteration training, and optimization of thinking expression based on your actual situation.
I wish you all the best to stay calm during your Jane Street interview, perform well, and get your offer soon!
