Jane Street ML Performance Engineer Interview Experience
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This post was last edited by sycstudent on 2025-09-26 12:41 Basic Information: Last year of PhD program in the Midwest (hopefully) I contacted a recruiter from JS during the conference and scheduled a
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This post was last edited by sycstudent on 2025-09-26 12:41 Basic Information: Last year of PhD program in the Midwest (hopefully) I contacted a recruiter from JS during the conference and scheduled an HR call and interview. Position: ML Performance Engineer I heard the second interview will test CUDA kernel performance. Does anyone have any good preparation materials to share? First Round Interview Results General
Coding Observing the posts on the forum, the first round of JS interviews seems to focus more on clarity and communication. The questions mainly involved implementing certain APIs, and weren't particularly difficult. Specific Questions: https://www.1point3acres.com/bbs/thread-1117783-1-1.html Class item has: optional
return the information of all current items. First Question: Given a map (item_name -> Item) representing all items to be purchased, where each item contains the buyer's desired price and buyer_name.
Return map(item_name -> price) representing the final transaction price. The final transaction price is the lowest price among items with the same name in the DataStore (and also lower than the buyer's desired price). Update is also required. Update DataStore It's straightforward, just write it according to the logic. Second question: After all transactions end for the day, some transactions may fail (e.g., credit card issues). Handle the following two scenarios: Scenario 1: Alice, item A, transaction price 100, transaction time 1000, transaction fails -> item A, 100 re-open to sell. Bob, item A, transaction price 110, transaction time 1010, transaction succeeds -> refund 10, and item A, 110 re-open to sell. Cathy, item A, transaction price 105, transaction time 1020, transaction succeeds -> nothing happens, because the 110 item A returned by Bob is higher than Cathy's original transaction price. Scenario 2: Alice, item A, transaction price 100, transaction time 1000, transaction fails. David, item A, bid 110, transaction time 1020, transaction fails (because it was out of stock at the time) -> charge. 100. The requirement is to return charge and refund information (buyer_name, refund/charge_amount) to all buyers. The question isn't difficult; the basic logic is to scan the transaction records chronologically, record any failed transactions, and compare them with subsequent successful transactions. It's quite tedious and requires communication with the interviewer on several details. How to obtain the transaction records in chronological order? How to know David's situation in scenario 2—that is, how do we know there was a buyer but the transaction wasn't sold? Scenario 2: If David's transaction is before Alice's in the chronological order, is a charge still needed? The interviewer said no. My answer to this question wasn't perfect, so I was timed out. She then asked me to ask her about JavaScript. Overall feeling: Not particularly difficult, but communication and clarity are crucial. I don't know the result yet. I haven't been on the forum for a long time, and I've run out of points. I hope you guys can give me some! Please!
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This question was reported by a candidate who interviewed at Jane Street. LeakCode aggregates interview reports from 10+ sources, including 1Point3Acres, Glassdoor, LeetCode Discuss, Blind, Reddit, Indeed, and Nowcoder. Each report is translated where necessary, deduplicated against existing entries, and tagged by company, role, round type, and reporting date.
Use this question as one calibration data point, not a memorization target. Companies typically rotate their question pools every 2-4 months; the exact wording of a 2024 question may differ from what you encounter today. The underlying pattern, difficulty level, and follow-up depth at Jane Street are the higher-signal extractions to take from this report.
For broader preparation context, the Jane Street interview process typically includes a recruiter screen, one or two technical phone screens, and a 4-5 round on-site loop covering coding, system design (at L4+ levels), and behavioral. Reports tagged on LeakCode show the round-by-round distribution and typical difficulty calibration. To browse questions filtered by round type and seniority, use the company hub linked above.
How To Practice This Type of Question
Solve similar problems on LeetCode under timed conditions (25-35 minutes per medium difficulty). The goal is pattern recognition: recognize the underlying technique (sliding window, two-pointer, BFS, memoized recursion, etc.) within 60-90 seconds of reading. Strong candidates verbalize their hypothesis out loud before coding, then iterate based on feedback. Weak candidates dive into implementation immediately, lose time on the wrong approach, and run out of time for follow-ups.
Companies update their question pools every 2-4 months. The exact wording of any given question may have been retired by the time you interview. Focus your prep on the pattern, not the specific problem. The patterns that appear in Jane Street reports consistently are the ones worth investing in; one-off niche problems are not.
During Your Jane Street Round
Apply the standard interview round template: clarify requirements (2-3 minutes), state your approach out loud and confirm direction with the interviewer (3-5 minutes), code with narration (15-25 minutes), test with concrete examples including edge cases (5 minutes), discuss optimization or trade-offs if time permits (5 minutes). This template is universally accepted across FAANG and adjacent companies; deviating from it produces weaker interviewer feedback signal.
The single most predictive failure mode in Jane Street reports tagged "no hire": not asking clarifying questions. Interviewers are explicitly trained to weight this. Strong candidates ask 3-5 clarifying questions even on problems that look obvious; weak candidates dive into code immediately. The clarifying-question check is often the first signal recorded in the interviewer's written notes.