Radix Trading Interview ProcessTier 1

High-Frequency Trading Firm - Chicago / NYC

49 practice questions → Apply at Radix Trading → Learn more about Radix Trading ↗ Report a question from your Radix Trading interview

problems

7 easy 29 medium 18 hard

hires: Quant Technologist, Quant Researcher

Recruiter / Screen

Phone - background + fit

An intro conversation about background and interest, sometimes with a quick technical warm-up.

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Editorial round — no practice problems.

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56 firmsEvery stageMust-do problems

C++ & Algorithms

60-90 min - coding

C++ implementation and numerical problems: reference-counted shared_ptr, fixed-buffer allocator, stable summation (Kahan), tournament min-comparisons.

Practice this round 40 problems →

#664 Wildcard Pattern Matching coding medium #985 Longest Subarray With Sum at Most K coding medium #1759 Longest Subarray With Sum K coding medium #2350 Largest Subset With Nonzero Bitwise AND coding medium #2515 Design a Sparse Matrix Class With Add and Multiply coding medium #2577 Implement a Reference-Counted Smart Pointer in C++seen 2014-01 coding medium #2586 Summing an Array with Vastly Different Magnitudes Accuratelyseen 2020-10 coding medium #2587 Fixed-Buffer Memory Allocator: rdx_malloc and rdx_freeseen 2014-01 coding medium #3321 Design a Temperature/Angle/Fixed-Point Value Class (Declarations Only)seen 2026-07 coding medium #3107 Streaming Moving Averageseen 2026-07 coding easy

Probability & Numerical

45-60 min - video Round guide →

Probability, combinatorics, and statistics with a numerical bent (variance computation, sampling).

Practice this round 40 problems →

#961 Finding the Heavy Bean With a Balance Scale combinatorics medium #18 Random Chord Length on a Unit Circleseen 2026-06 probability medium #1460 Online Outlier Detection in a Data Stream statistics medium #2589 Uniformly Sampling a Returning Random Walk Pathseen 2023-04 combinatorics medium #200 Perfectly Balanced Dice Rolls probability medium #2585 Catastrophic Cancellation in Computing the Variance of n + U(0,1)seen 2020-10 statistics medium #565 Color Combinations When Drawing Balls combinatorics easy #329 Arrival Order Probability Across Cities probability medium #898 Chocolate Bar Breaksseen 2022-06 combinatorics easy #365 Even vs. Odd Heads: Does Symmetry Force Fairness? probability medium

Linear Algebra & Optimization

45-60 min - research Round guide →

Linear algebra (eigenvalues, conditioning), optimization (LP/least-absolute-deviations), regression, and stochastic processes.

Practice this round 40 problems →

#1395 Eigenvalue-Determinant-Trace Relationship linear-algebra medium #1188 Optimal Kelly Fraction for an Asymmetric Bet optimization medium #2510 The Closed-Form OLS Solution and When It Existsseen 2023-04 regression medium #2382 Expected Flips Until Two Heads in a Row stochastic-process medium #1988 Inverse of an Equicorrelation Matrix linear-algebra medium #2590 Minimizing a Sum of Absolute Values via Linear Programmingseen 2023-04 optimization medium #2583 Eigenvalues and Conditioning of a Cyclic Permutation Matrixseen 2020-10 linear-algebra medium #2584 Recurrence and Numerical Stability for the Integral of x^n e^xseen 2020-10 linear-algebra medium #3318 Numerically Inverting a Matrix and Its Complexityseen 2026-07 linear-algebra medium

Onsite - Hardest Rounds

Final rounds - the toughest reported problems

The hardest reported Radix Trading problems across every topic. (Hard-rated only; earlier rounds cover easy/medium, so nothing repeats.)

Practice this round 40 problems →

#606 Maximum Profit with Two Transactions coding hard #2053 QR Factorization via Householder Reflectors linear-algebra hard #1461 Optimal Stopping on a Fair Coin Random Walk optimization hard #788 Identifying Poison With Multiple Tasting Roundsseen 2022-06 probability hard #2077 Scoring Rules and Model Calibration for Trading Classifiers statistics hard #2497 Drunkard's Walk: Probability of Escaping to Infinity stochastic-process hard #1646 Order Management System with Price-Time Priority Matching coding hard #2082 Shrinkage Estimator for Correlation Matrix linear-algebra hard #1774 Optimal Interval Scoring Under a Coverage Constraint optimization hard #1392 Divisibility of Dice Sums by 6 and 7 probability hard #2197 Wald Test for Sharpe Ratio Equality Under Serial Correlation statistics hard #1648 Order-Statistics Tree coding hard

The day before

C++ & Algorithms
Probability & Numerical
Linear Algebra & Optimization
Onsite - Hardest Rounds

Cheatsheet →

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Radix Trading round-by-round guides

Radix Trading interview guide: the firm, culture, roles and pay →

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

Radix Trading interview — FAQ

What is the Radix Trading interview process?

Radix is a secretive Chicago HFT firm with a Quant Technologist model. Expect hard C++/algorithms, numerical-analysis problems (stable summation, catastrophic cancellation, custom allocators), plus probability and linear algebra. No game. The loop runs 5 stages: Recruiter / Screen, C++ & Algorithms, Probability & Numerical, Linear Algebra & Optimization, Onsite - Hardest Rounds.

How many rounds does Radix Trading have?

5 stages in total, starting with the Recruiter / Screen and ending with the Onsite - Hardest Rounds.

How do I prepare for the Radix Trading interview?

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