The Voleon Group Interview ProcessTier 2

Machine-Learning Quant Fund · Berkeley, CA

49 practice questions → Apply at The Voleon Group → Learn more about The Voleon Group ↗ Report a question from your The Voleon Group interview

problems

5 easy 38 medium 9 hard

hires: Software Engineer, ML Research Staff, Data Scientist

Online Assessment (SWE + Data tracks)

Voleon is a Berkeley-based ML/systematic asset manager; hiring is academic (statistics & ML a stats/DS PhD knows cold). The OA is coding/take-home: a flagship exchange-sim coding challenge, sub-grid and string problems, and a data-analyst SQL + pandas task. Research interviews go deep on stats and ML.

Practice this round 6 problems Pro

Engineering / Research

current

2023 -> 2026

Coding OA / take-homestdin/stdout, 1-1.5 hr5 problems

The coding OA mixes a custom exchange/execution sim (trailing-minute volume, participation-rate execution) with classic problems (largest bounded sub-grid, group anagrams, file parsing, an increment-stack). Auto-graded below.

Group AnagramsThe whole problem collapses once you see that anagram-ness is just equality of letter counts. Hash each word down to its count signature and words falCodingEasySolve →File I/O: Count Quantities From an Input FileA dictionary that remembers insertion order is exactly the right tool: it gives O(1) accumulation per line and free first-appearance ordering, so you CodingEasySolve →Berkeley Exchange: Trailing-Minute Volume TrackerPicture a sliding 60-second window dragged along the timeline for each ticker. As the window's right edge advances to the query time, trades fall off CodingMediumSolve →Largest Square Subgrid With Every Block Under a BudgetReported in this firm OA; auto-graded.CodingMediumSolve →see all 5 problems →

Data Scientist / Analyst

current

2023 -> 2026

Data Analyst OA (SQL + pandas)1 hr, 5 questions1 problem

The Data Analyst OA is 4 SQL + 1 pandas aggregation (high bar). The pandas aggregation/filter task is auto-graded below.

Pandas Aggregation and FilteringPandas Aggregation and FilteringCodingMediumSolve →

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Phone / Tech Screen (SWE track)

45–60 min · HackerRank / phone Round guide →

One hard LeetCode-style problem + an optimization follow-up, read from stdin / written to stdout with real test cases. The single highest-frequency item is the Basic Calculator series (+−, then ×÷, then parentheses, then variable substitution, then resolving a dict of inter-dependent variable expressions via topological sort).

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#2514 Expression Evaluator With Variables and Dependenciesseen 2020-03 coding hard #664 Wildcard Pattern Matchingseen 2018-10 coding medium #2521 Maximum Concurrent Intervals Over a Small Integer Rangeseen 2023-03 coding medium #1599 LFU Cacheseen 2019-07 coding hard #1759 Longest Subarray With Sum Kseen 2019-11 coding medium #1600 LRU Cache coding medium #996 Merging Overlapping Intervalsseen 2023-03 coding medium #608 Minimum Number of Rooms for Interval Partitioning coding medium

Onsite / VO (SWE track)

4 rounds · 1hr + 2.5hr coding + design Round guide →

Hard SWE loop: Word Search II (N×N, M words, 8 directions, stdin/stdout; Trie+DFS pruning vs TLE). Core: 4-part order-matching engine (limit→market→stop→cancel; heaps, clean code). Whiteboard: sparse matrix (add/multiply) or hashmap internals. System design: huge-map point→country (quadtree), dependency resolution, distributed crawler.

Practice this round 20 problems →

#2517 Word Search on a Grid With Eight Directions and Pruningseen 2019-11 coding hard #2518 Build an Order-Matching Engine: Limit, Market, Stop, Cancelseen 2020-03 market-microstructure hard #2520 Trailing-Volume Tracking and Participation-Rate Executionseen 2025-12 market-microstructure hard #2519 Kac Ring: O(1) Color Ratio After Many Stepsseen 2025-08 coding hard #664 Wildcard Pattern Matchingseen 2018-10 coding medium #1599 LFU Cacheseen 2019-07 coding hard #2514 Expression Evaluator With Variables and Dependenciesseen 2020-03 coding hard #1647 Order Matching Engine Designseen 2020-03 coding hard

ML Research Phone (QR track)

~60 min · stats + ML Round guide →

Stats + ML phone after a reading list (~10 intro, 40 tech, 10 Q&A): OLS closed form, when (XᵀX)⁻¹ exists, gradient-descent least squares in basic numpy, R²-combining, Y~X vs X~Y slope puzzles, E[X|X+Y] for joint normals. Doubly-stochastic matrices, small-sample binomial median test, maybe one numpy coding task.

Practice this round 26 problems →

#2522 Upper Bound on Joint R-Squared From Pairwise Correlationsseen 2021-10 regression hard #2504 Conditional Expectation of One Normal Given the Sumseen 2020-09 random-variables medium #2510 The Closed-Form OLS Solution and When It Existsseen 2025-10 regression medium #2523 The Optimal Step Size for Gradient Descent on a Quadraticseen 2020-06 optimization medium #2524 Choosing K in KNN and the Bias-Variance Tradeoffseen 2020-11 machine-learning medium #348 Conditional Expectation of a Linear Combination Given a Sumseen 2020-11 expectation medium #1840 Deriving the OLS Estimator regression medium #1543 Computing OLS When the Design Matrix Is Too Large for Memoryseen 2025-10 linear-algebra medium

Research VO + Deep-Dive (QR track)

2 × 2 hr · stats / ML / coding / research Round guide →

VO Part 1: a statistics round and an ML round (interviewers are a stats PhD + a same-field PhD), including hands-on 'run the data' in R/pandas (regression, p-values, debugging weird data setups). VO Part 2: a coding round (ex-CS-professor interviewer) and a research deep-dive where a senior researcher probes your PhD work. Fit matters a lot.

Practice this round 24 problems →

#2522 Upper Bound on Joint R-Squared From Pairwise Correlationsseen 2021-10 regression hard #2506 Two Heads in a Row Before the Other Player's First Tailseen 2025-11 probability hard #2519 Kac Ring: O(1) Color Ratio After Many Stepsseen 2025-08 coding hard #1866 OLS Assumptions, Violations, and Diagnosticsseen 2020-10 regression medium #1543 Computing OLS When the Design Matrix Is Too Large for Memoryseen 2025-10 linear-algebra medium #2510 The Closed-Form OLS Solution and When It Existsseen 2025-10 regression medium #2507 Testing a Median With No Distributional Assumptionsseen 2020-11 statistics medium #2058 Range of R-Squared in Multiple Regressionseen 2020-11 regression medium

Culture / Intro Discussion (all tracks)

~30–45 min · technical manager Round guide →

A 2025 addition, a culture/intro discussion with a technical manager or hiring manager: opinions on engineering/ML, behavioral (a proud project, a data-driven decision), and weaknesses. It's a non-trivial gate, not a formality. Reported on both the SWE and QR tracks.

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Editorial round — no practice problems.

References + Background Check (all tracks)

3 references · background check

Aggressive closing gates: three references (award-heavy probing for research) plus a background check. Candidates who pass the technical loop are frequently rejected here, so it's a real step.

Practice this round →

Editorial round — no practice problems.

The day before

Basic Calculator series (parentheses + variable-dependency toposort)
Word Search II (Trie + DFS pruning, stdin/stdout)
Order-matching engine (limit/market/stop/cancel via heaps, clean code)
Sparse-matrix class + quadtree map-lookup design
OLS/logistic derivations; R²-combining + Y~X vs X~Y; E[X|X+Y]
Hands-on R/pandas: regression, p-values, debugging data

Cheatsheet →

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The Voleon Group round-by-round guides

The Voleon Group interview guide: the firm, culture, roles and pay →

Stage guides for every firm: superdays · behavioral questions · market-making games

The Voleon Group interview — FAQ

What is the The Voleon Group interview process?

Voleon: machine-learning-first quant fund with NO trading game; its 'stock exchange' content is coding an order-matching engine, not a live sim. SWE: hard, production-quality stdin/stdout coding (Basic Calculator, Word Search II, sparse-matrix class). ML Research: statistics + ML derivations, hands-on data work. Very high bar; aggressive reference/background checks cull even passing candidates. The loop runs 7 stages: Online Assessment (SWE + Data tracks), Phone / Tech Screen (SWE track), Onsite / VO (SWE track), ML Research Phone (QR track), Research VO + Deep-Dive (QR track), Culture / Intro Discussion (all tracks), References + Background Check (all tracks).

How many rounds does The Voleon Group have?

7 stages in total, starting with the Online Assessment (SWE + Data tracks) and ending with the References + Background Check (all tracks).

How do I prepare for the The Voleon Group interview?

Work the stage notes above, then drill the The Voleon Group interview-questions set and the The Voleon Group online-assessment practice — each problem has a full worked solution.