PRACTICE GUIDE HRT
HRT Coding Problems Practice Test
The HRT coding problems screen is 4 questions in 70 minutes - about 17.5 minutes each - answered by typing the number, with no calculator. There is no negative marking, so leaving an item blank gains you nothing over guessing.
Where it sits: First technical round. The practice sitting on this page runs the same item count, the same clock and the same marking rule, with questions generated by Outcry rather than taken from Hudson River Trading.
Candidates report algorithm and systems questions closer to competitive programming than to standard software interviews.
Outcry is not affiliated with Hudson River Trading and has no access to their assessment content. This guide describes an assessment format that candidates report publicly; the questions here are generated by Outcry and are not Hudson River Trading’s own.
What it screens
An automated trading firm known for research-driven strategies and a heavy C++ and algorithms bar.
- ✓Reading concurrent code and pointing at the defective line
- ✓Order-book data structures: what happens on a cross, a cancel, a partial fill
- ✓Algorithmic complexity chosen for the input sizes stated in the problem
- ✓Monte Carlo methods and when a simulation beats a closed form
Where it sits at Hudson River Trading
This section does not arrive on its own. It opens the paper, and the sitting around it runs 85 minutes and 14 items in total, with Code review on the same continuous clock. Candidates who prepare only for this round tend to be caught by the pacing of the rest.
There is no going back. You answer or skip, and the next item loads, which means the decision to leave an item is final at the moment you make it.
The format
These are the numbers the HRT sitting on this site runs on, matching the format candidates report.
| Questions | 4 |
|---|---|
| Time | 70 minutes |
| Per question | 17.5 minutes |
| Negative marking | No |
| Answer style | Typed numeric answer, no calculator |
| Where it sits | First technical round |
What it tests, with a worked example
Every example below is generated by Outcry, drawn from the same question generators the timed drills run. None of them is Hudson River Trading’s.
Data structure implementation
Build the thing rather than call it: an order book, a cache, a ring buffer. Graded by hidden tests, so there is no partial credit for an approach.
Language and systems detail
Memory, references, undefined behaviour and the things that bite in production.
Example
Frames: 3 Reference string: 1 0 1 0 1 0 0 1 5 0 0 1
A process makes the page references below against 3 free frames, using FIFO replacement. How many page faults occur?
- 9
- 2
- 3
- 4
Answer 3
FIFO evicts the oldest resident page regardless of use. Walking the string gives 3 faults and 9 hits over 12 references. The first 3 references are always faults because the frames start empty.
Numerical and data handling
Floating point, aggregation and joins on data that does not fit the obvious shape.
Example
x 12 22 7 18 23 5 17
What is the sample variance of the series above? Use the n-1 denominator.
Answer 49.8095238095238
The mean is 14.86. Squared deviations: 8.16 + 51.02 + 61.73 + 9.88 + 66.31 + 97.16 + 4.59 = 298.86. Divided by n-1 = 6 that is 49.81. The n denominator would give 42.69.
Edge cases
Empty input, one element, duplicates and overflow. The hidden tests always include them.
Statistics in code
Rolling windows, correlations and quantiles, implemented rather than imported.
Example
2% of order flow is toxic. A classifier catches 90% of toxic flow and also fires on 5% of clean flow. An order just fired the classifier. What is the chance it is toxic?
- 26.9%
- 95%
- 2%
- 90%
Answer 26.9%
Take 10,000 orders. 200 are toxic and 180 of those fire. 9,800 are clean and 490 of those fire anyway. So 180/670 ≈ 26.9%. The classifier's 90% catch rate is not the answer - the base rate dominates.
Reading a spec precisely
Return type, ordering and tie-breaking are graded, and are where most silent failures come from.
What a good score looks like
On a paper of 4 questions with no penalty for a wrong answer, the only thing an unanswered question can do is cost you. Coding screens are usually pass-fail on hidden tests rather than scored, and candidates commonly report that a solution passing every correctness test still fails on a timeout. Treat full marks as solving every problem inside the complexity bound, not merely solving it.
How to train for it
- 01Implement the core structures from scratch once each. The screens ask you to build them, not use them.
- 02State the complexity before you write. If it is worse than the input size allows, the approach is already wrong.
- 03Practise without an autocomplete. The screens run in a bare editor, and the gap between writing code with help and without it is larger than most people expect.
TRAIN IT HERE
The drills that match each section
Concurrency Clash
Find the data race, name the fix - real C++ defect patterns, five levels.
Order Book
Matching-engine mechanics: crosses, cancels and partial fills.
Algorithm Lab
DP tables, Monte Carlo estimation and speed rounds at four difficulty tiers.
SIT THE FULL BATTERY
All the sections back to back on one clock, marked the way the real screen marks them, with a by-skill breakdown at the end. Included with any pass.
Also reported at Hudson River Trading
Common questions
- Is the HRT coding problems test multiple choice?
- Typed numeric answer, no calculator. You type the number, so there is nothing to eliminate your way to.
- How long is the HRT coding problems test?
- 4 questions in 70 minutes, which is about 17.5 minutes each.
- Is there negative marking on the HRT coding problems test?
- No. A wrong answer costs nothing beyond the mark you would have earned, so leaving an item blank is never better than guessing at it.
- How do I practise for it free?
- Every drill linked on this page is free to play, with no account, inside a daily run cap. Questions are generated fresh each run, so there is nothing to memorise between attempts. The full Quant Developer Online Assessment sitting puts the sections back to back on one clock.