Jane Street Interview Questions
Practice 53 real Jane Street interview questions for 2026 — Jane Street interview questions and interview preparation built from real problems used in actual interviews with detailed solutions. This collection emphasizes coding-first assessment, trading-flavored probability and puzzle questions, and ML/statistics tasks that mirror the firm’s focus on precision, speed, and clear reasoning. Expect short, whiteboard-style problem solving and paired coding that tests correctness, edge-case thinking, and clear verbalization of tradeoffs; prepare by sharpening algorithmic coding, probability modeling, time-series intuition, and concise system designs. Software engineering content dominates: problems repeatedly ask you to transform sparse time-stamped streams into dense rows, validate and canonicalize order-book/trade data across databases, and design low-latency message flows between exchanges and trading systems, plus implementation puzzles (e.g., Connect Four) and probability/game-theory questions. Data scientist questions cluster around real-vs-fake DNA classifiers, probability and queueing puzzles, and trading RFQ competitiveness analysis. Machine learning engineering questions focus on end-to-end training frameworks, time-series forecasting for trading, and small runtime/compiler design for domain-specific languages.
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Optimal Stopping with Square-Number Ruin
Optimal Stopping with Square-Number Ruin You repeatedly roll a fair six-sided die and add each roll to a running total. Before each roll, you may stop...
Optimize a Two-Box Place-or-Take Game
Optimize a Two-Box Place-or-Take Game A one-player game has two opaque boxes and lasts exactly 100 turns. On a place turn, a third party adds one unit...
Solve probability and game-theory puzzles
You are interviewing for a quant trading internship. Work through the following probability and game-theory puzzles. There is no need to answer instan...
Validate order book data across multiple databases
Assume your organization stores order book–related data in multiple databases (e.g., one for raw exchange messages, one for normalized orders, one for...
Turning Interview Code into a Reusable Library or API
You have just finished implementing a small game engine during a coding interview: a board data structure for a two-player piece-dropping game, a func...
Design exchange–trading system message flow
Design the message contract and flow between a firm's trading system (OMS/EMS) and an external exchange. Assume: - The trading system sends orders and...
Design a Real-vs-Fake DNA Classifier
Question You are given DNA sequences over the alphabet {A, C, G, T}, where sequence lengths may vary. You have: - a small labeled dataset containing b...
Build a time-series forecasting model
Build a time-series forecasting model Forecast the Next H Steps for Time Series Context You are given one or more time series with timestamps and nume...
Collapsible Code Editor: Brace Matching and Toggle
This question tests stack-based parsing and stateful data structure design through a two-part brace-matching and collapsible editor problem. It evalua...
Calculate win chance in three-player dice game
Probability of Winning with Rerolls on Ties Setup - Three players: A (you), B, and C. - A fair six-sided die is used. - B and C have already rolled an...
Alternating Die-Roll Game: Optimal Accept/Reject Strategy
Two players, A and B, play the following game with a fair 21-sided die whose faces are labeled with the integers $-10, -9, \ldots, 9, 10$ (one integer...
Implement a Circular Buffer
This question evaluates understanding of data structures and buffer management, specifically FIFO semantics, fixed-capacity storage, wraparound indexi...
Design and implement a tiny language runtime
Design and implement a tiny language runtime Minimal Imperative Language — Design and Implementation Task Context You are asked to design and implemen...
Design sequential reveal classification and policy
FashionMNIST: Row-wise Reveal Evaluation, Reward-Optimal Masking, Augmentation, and Early Exit Context You have a trained CNN classifier for FashionMN...
Transform sparse time-code stream to dense rows
Problem You are given: - A fixed set of M distinct codes (strings). The column order of the output matrix is the lexicographic order of these codes. -...
Code Editor with Block Shrink and Expand (Code Folding)
Implement the core of a code editor (similar to VS Code) that supports code folding: collapsing ("shrink") and restoring ("expand") indentation-based ...
Design an end-to-end training framework
Design an end-to-end training framework Design an End-to-End Time-Series Forecasting Framework (PyTorch) You are tasked with designing a production-gr...
Implement compiler for custom language
Implement compiler for custom language Design and implement a simple compiler/interpreter Goal Design and implement a small compiler/interpreter for a...
Predict future time-series values
Predict future time-series values End-to-End Time-Series Forecasting (PyTorch) Context You are given one or more regularly sampled numeric time series...
Answer why Jane Street
HR Screen Behavioral Question: Why Jane Street? You are interviewing for a Software Engineer role. In 60–90 seconds, explain: 1. Why Jane Street speci...