Coding OA Patterns at Citadel, HRT, and Jane Street: 2026 Prep Playbook

Coding Online Assessment (OA) Patterns at Citadel, HRT, and Jane Street: 2026 Prep Playbook

The coding online assessment is the most-feared filter in quant interview funnels. At Citadel Securities, Hudson River Trading (HRT), Jane Street, and several peer firms (Two Sigma, Optiver, Jump), the OA is timed, monitored, and unforgiving — bombing it ends the process before you talk to a human. The good news: OAs across these firms share recognizable patterns. Strong preparation closes the gap between candidates with similar academic backgrounds. This guide covers what each firm’s OA actually looks like in 2026, the question patterns that recur, and the prep approach that converts.

What’s the OA Format at Each Firm

Jane Street

Jane Street is the lightest-OA shop of the top three. Most candidates start with a recruiter call and a take-home thinking exercise rather than a strict timed coding test. Some candidates encounter:

An OCaml-flavored functional reasoning problem (the firm uses OCaml internally, but you can solve in any language)
A short coding exercise emphasizing clean correctness over algorithmic gymnastics
For SWE / quant developer roles: a HackerRank-style 60–90 min OA with 2–3 problems

Jane Street emphasizes mental math separately (in person or video) and tests probability conceptually. The coding OA is less the gating round here than at Citadel Securities or HRT.

Citadel Securities (and Citadel)

Citadel uses HackerRank for most coding OAs. Format varies by role and team but typically:

70–90 minutes, 2 problems
Difficulty: 1 medium + 1 hard (LeetCode equivalent: medium-hard to hard)
Languages allowed: most major languages (C++, Python, Java, JavaScript, Go, etc.)
Problems mix data structure / algorithm classics with quant-flavored variations (signal processing, probability sequences, market data parsing)
For quant roles: an additional probability / statistics OA may be administered separately

Citadel Securities is more rigorous than Citadel (the hedge fund) on the coding OA — the market-making business demands strong real-time engineering, so coding bar is higher.

Hudson River Trading (HRT)

HRT’s OA is one of the toughest in the industry:

90 minutes, 1–2 problems on HackerRank or similar platform
Difficulty: hard to very hard (LeetCode hard equivalent or beyond)
Strong emphasis on C++ specific behavior, performance, low-level details — though most languages are allowed
Problems often have 5–10 sub-tasks with progressively harder constraints
For software engineer roles: substantial focus on systems / performance reasoning
For quant researcher roles: probability / statistics OA in addition to coding

HRT’s OA pass rate is reportedly very low (5–10% of candidates). Strong CS-Olympiad-trained candidates clear it; average Big Tech candidates often don’t.

Two Sigma, Jump, Optiver, IMC, SIG

Each has its own variation but generally mirror the Citadel pattern: 60–90 minutes, 2–3 medium-to-hard problems on a HackerRank-style platform. SIG and Akuna emphasize game / probability questions more (as expected from options market makers); Optiver emphasizes mental math separately.

The Question Patterns That Recur

Pattern 1: Array / sequence manipulation under time pressure

Classic LeetCode patterns appear in OAs:

Two-pointer / sliding window (substring problems, max subarray)
Sorting + post-processing (merge intervals, partition problems)
Hash-map counting (frequency questions, anagrams)

Why they appear: solid filter for “can you code at all” without requiring deep finance domain knowledge. Most OAs include at least one problem in this bucket.

Pattern 2: Dynamic programming with twist

Classic DP problems with an unusual constraint or modification:

Coin change variants (minimum coins, count ways, with restrictions)
Edit distance variants (minimum operations, with special operations)
Knapsack variants (bounded knapsack, multi-dimensional knapsack)
Sequence alignment / longest common subsequence variations

Citadel and HRT particularly love DP problems where the recurrence is non-obvious. Strong candidates recognize the DP structure quickly; weak candidates flounder.

Pattern 3: Order book / market data parsing

Increasingly common at trading firms (Citadel Securities, HRT, Jump):

Parse a stream of order book updates and answer questions about state at time T
Process trades and compute statistics (VWAP, time-weighted average price, profit / loss given a sequence)
Handle order matching with limit orders, market orders, cancellations

The pattern: read input carefully, maintain a data structure (often a priority queue or sorted data structure), update it efficiently. Tests data structure choice plus careful state management.

Pattern 4: Probability and expectation simulation

Asked at firms with quant emphasis (Two Sigma, Citadel, HRT, SIG):

Simulate a stochastic process and report expected value
Implement Monte Carlo for a problem with no closed form
Compute probabilities of compound events

The trap: candidates with weak probability fundamentals write inefficient simulations or fail to reason about variance / convergence.

Pattern 5: Graph / tree algorithms with constraints

Classic graph problems with unusual constraints:

Shortest path with edge weight modifications (Dijkstra variants)
Minimum spanning tree with constraints (must include / exclude edges)
Strongly connected components, topological sort with multiple valid orderings
Tree problems: lowest common ancestor, tree DP, path queries

HRT particularly loves these. The pattern: standard algorithm + clever data structure choice.

Pattern 6: Bit manipulation and number theory

Less common but appears occasionally:

Bit manipulation tricks (XOR sums, popcount, bit DP)
Modular arithmetic (Fermat’s little theorem, modular inverse)
Prime sieving and applications

These are signaling questions — candidates who clear them quickly have stronger fundamentals than the average.

Pattern 7: Implementation-heavy with no clever trick

Some OAs include a long, careful-implementation problem with no algorithmic insight required — just thorough coding, edge cases, and careful state management. Tests whether you can write production-quality code under pressure.

Prep Approach That Converts

Months 1–2: Fundamentals

Solve 100–150 LeetCode mediums across all the major topics: arrays, strings, linked lists, trees, graphs, DP, greedy, two-pointer, sliding window, hash maps
Goal: solid recognition of common patterns and ability to implement standard algorithms in your chosen language at speed
Practice in HackerRank-style timed mode for at least 30–50 of these

Months 2–3: Hard problems and pattern recognition

Solve 30–50 LeetCode hards, focusing on DP and graph problems
Read editorial / discussion solutions to learn alternative approaches
Time yourself — at this stage you should clear most LeetCode hards in under 45 minutes

Months 3–4: Firm-specific patterns

Practice on HackerRank’s “Interview Preparation Kit” tracks specific to your target firms
For trading firms: practice market data / order book problems (some are on HackerRank’s “Hourrank” archive)
Take 5–10 timed mock OAs under real conditions (90 min, no breaks, no IDE assistance, no AI)

Final 2 weeks: Rest and review

Stop solving new problems. Review your weak spots.
Revisit your saved solutions to LeetCode hards in your weak topic areas.
Take one final timed mock OA 3–5 days before the real one.
Sleep well the night before.

What to Do During the OA

The first 5 minutes: read everything

Before writing any code, read both problems carefully. Understand what’s being asked, what the input format is, what the constraints are. Many OAs have a “trap” — a problem that looks like it needs a complicated algorithm but actually has a simple greedy solution if you read carefully.

Solve the easier problem first

If problem 1 is medium and problem 2 is hard, solve problem 1 first to lock in the points. Then attempt problem 2. Attempting the hard problem first risks running out of time having scored zero on either.

Test as you go

Run sample test cases as you write. Don’t write the entire solution and then run it — test incrementally. Each minute spent debugging at the end is a minute not spent on the second problem.

Watch the time

Set a mental checkpoint: if you’re 30 minutes in and haven’t started problem 2, move on. Partial credit for problem 2 likely beats perfect on problem 1 alone.

Don’t optimize prematurely

If you have a working O(n²) solution and the constraints suggest O(n log n) is needed, submit the O(n²) first to get partial credit on small test cases, then optimize. Don’t let perfect be the enemy of done.

Common Mistakes

Skipping the constraints section. Constraints tell you the time complexity needed and what edge cases matter.
Writing 100 lines of code without testing. Test after every 10–15 lines.
Choosing the wrong language. Use whichever language you’re fastest in. Don’t use C++ to “look impressive” if Python is your best language.
Panicking on a hard problem. Step back. Often there’s a small insight you’re missing. If 10 minutes pass with no progress, move on or simplify your approach.
Ignoring partial credit. If you can’t solve the full problem, at least handle the simple cases for partial points.

Frequently Asked Questions

Can I use AI assistants during the OA?

No. Most firms explicitly prohibit AI tools during the OA and use proctoring software (camera, screen recording, browser lock). Citadel, HRT, Jane Street, Two Sigma all proctor. Using AI is grounds for immediate rejection and can be flagged in industry hiring databases. The risk-reward isn’t there.

What language should I use?

Use whichever you’re fastest in. Python is most common (concise syntax, fast iteration); C++ is favored at HRT and some HFT firms (familiarity with their stack); Java is acceptable everywhere. Don’t switch languages right before the OA — stick with what you’ve practiced in.

How many candidates pass the HRT OA?

Reported pass rates are very low — 5–10% of candidates who attempt the OA pass to the next round. The bar is genuinely tough; even strong Big Tech engineers often don’t clear it. Calibrate prep accordingly — HRT’s OA is closer to ICPC / Codeforces difficulty than typical FAANG OAs.

Can I retake an OA if I bomb the first time?

Most firms have a 6–12 month cooldown before re-applying. Some firms explicitly track candidates who didn’t pass and apply a higher bar on re-application. Not impossible to recover but meaningfully harder. Better to over-prepare the first time.

How does Jane Street’s OA differ from the others?

Jane Street is lighter-OA in their funnel — more emphasis on take-home thinking exercises and OCaml-flavored functional reasoning than strict 90-minute timed coding tests. The overall bar is comparable to Citadel and HRT but distributed across different filters.