Voleon Group Interview Questions
Machine-learning, statistics, regression, probability, and linear-algebra problems drawn from Voleon Quant/ML Researcher interviews, plus the coding tasks that back them.
Inside the Voleon Group interview
Voleon Group is a Berkeley-based machine-learning-first systematic hedge fund that applies statistical learning to financial markets. Its Quant/ML Researcher interviews are unusually regression-heavy and probe whether you can reason from first principles about statistics, ML, probability, and linear algebra — not just recite results.
What they test
The center of gravity is regression and statistics: deriving the OLS estimator, its closed-form solution and when it exists, the assumptions and their violations, L1 vs. L2 regularization, and sharp facts about R-squared and reverse regressions. Around it sits a real machine-learning block (KNN bias-variance, choosing K, regression-tree splits, logistic-regression perturbations, k-means) and a probability / expectation core (conditional expectations of normals given a sum, dice and coin problems, random walks). Linear algebra ties it together — out-of-core OLS, fitting hyperplanes, structured-matrix properties.
The recurring shapes
Expect derive-and-bound questions: write down an estimator, then characterize when it's defined, what it converges to, or how a perturbation moves it. Several problems push on the two-sided regression idea (slope of Y-on-X vs X-on-Y, joint vs pairwise R-squared bounds). A second strand is scalable numerics — computing OLS when the design matrix won't fit in memory, optimal gradient-descent step sizes on a quadratic, sparse-matrix and matrix-chain operations — reflecting a fund that ships ML at scale.
How to approach
Be ready to do the algebra live and state assumptions out loud: when is XTX invertible, what regularization buys you, how bias trades against variance. For the coding tasks (caches, interval merging, order-matching, pandas aggregation, sparse matrices), aim for clean, correct implementations with the right data structure rather than clever tricks. Treat every probability question as a chance to show clean conditioning and expectation reasoning.
The mix leans heavily medium, with a handful of hard coding-and-microstructure builds and a few easy warmups to settle in.
Voleon Group coding questions (20)
- Design a SuperStack With a Bulk-Increment Operation
- Berkeley Exchange: Trailing-Minute Volume Tracker
- Group Anagrams
- Pandas Aggregation and Filtering
- File I/O: Count Quantities From an Input File
- Kac Ring: O(1) Color Ratio After Many Steps
- Merging Overlapping Intervals
- Maximum Concurrent Intervals Over a Small Integer Range
- Grouped Mean and Weighted Mean in Pandas
- Minimum Cost of a Matrix Chain Product
- Order Matching Engine Design
- Expression Evaluator With Variables and Dependencies
- Word Search on a Grid With Eight Directions and Pruning
- Longest Subarray With Sum K
- Design a Sparse Matrix Class With Add and Multiply
- Largest Square Subgrid With Every Block Under a Budget
- LFU Cache
- Wildcard Pattern Matching
- Minimum Number of Rooms for Interval Partitioning
- LRU Cache
Voleon Group regression questions (9)
- The Closed-Form OLS Solution and When It Exists
- R-Squared Bounds for a Joint Regression
- Upper Bound on Joint R-Squared From Pairwise Correlations
- Range of R-Squared in Multiple Regression
- OLS Assumptions, Violations, and Diagnostics
- Range of the Reverse Regression Slope
- L1 vs. L2 Regularization
- OLS Slopes of Y on X vs X on Y
- Deriving the OLS Estimator
Voleon Group probability questions (4)
Voleon Group machine learning questions (4)
Voleon Group linear algebra questions (3)
Voleon Group optimization questions (3)
Voleon Group market microstructure questions (2)
Voleon Group expected value questions (2)
Voleon Group statistics questions (1)
Voleon Group random variables questions (1)
Voleon Group stochastic processes questions (1)
Voleon Group interview FAQ
What kind of questions does Voleon Group ask in quant interviews?
Candidates most often report coding, regression and probability questions. This page collects 50 of them, 43 stamped with the month they were last reported — each with a full worked solution.
How hard are Voleon Group interview questions?
The set spans 4 easy, 37 medium and 9 hard problems. Most sit at medium difficulty — solvable in a few minutes with clean reasoning — with a harder tail that rewards knowing the canonical tricks.
How do I prepare for the Voleon Group quant interview?
Work through this set by topic (use the sidebar), starting from your weakest area. 7 problems are free to open with their full solution, so you can judge the quality before anything else. Then walk the full Voleon Group interview guide for the round-by-round funnel and the online assessment.
Are these the actual Voleon Group interview questions?
They are built from candidate-reported Voleon Group questions. We rewrite each prompt for clarity and author the worked solutions ourselves — we don't claim the wording is verbatim, and we never invent questions or recycle generic lists. 43 of 50 carry the month they were last reported.