nearest (of locations) Citadel Citadel Securities has been sending out OA like crazy, and many students received written test invitations not long after submitting their resumes, and the overall pace is very tight, no matter it is for Quant, Software Engineer or Data positions. In this article, we will give you a full account of the Citadel OA question types, question styles and high-frequency test points, and combine them with Programhelp's real coaching cases to help you grasp the key to seize the qualification of one side.
OA Invitation Cadence & Platform Description
Most of Citadel's OA is conducted through the HackerRank platform, and there is usually a 3-5 day validity period for answering the questions after receiving the invitation, and you can't quit in the middle once the timer starts. The whole exam is a combination of "algorithm + mathematical logic + engineering practice", with high quality questions and strict grading, so it's not suitable for naked exams.
The 5 students we recently mentored all received OA's in July for positions including:
- Software Engineer - New Grad
- Quantitative Researcher - Full-time
- Data Science Intern
Each student received a slightly different type of question, but the style was highly consistent and is broken down in detail below 👇
Citadel OA Real Questions Sharing
2. Decision Tree Update Feasibility
Modified Question.
You've spent the past week optimizing a decision tree model using 50 GB of training data. After the weekend, you are informed that another 12 GB of data is now available and must be included in the model. After the weekend, you are informed that another 12 GB of data is now available and must be included in the model. A new evaluation report is due later today. How feasible is this task and why?
A. Not feasible: loading 12 GB more data will exceed memory limits
B. Not feasible: decision trees must be fully rebuilt with new data
C. Feasible: just stream the 12 GB into the existing model to update it
D. Feasible: since performance was already excellent, the extra data won't matter
E. Feasible: you could switch to a faster model like logistic regression
4. SVM and Imbalanced Feature Distribution
Modified Question.
You're using a dataset with a single feature-average daily speed on a highway. If the average speed is above 75 km/h, there are no crashes. If it's below 75 km/h, there is always at least one crash. Your teammate says an SVM might not work well because speed values are unevenly distributed. Your teammate says an SVM might not work well because speed values are unevenly distributed.
A. Yes - SVMs are sensitive to feature distribution imbalance
B. No - SVMs focus on support vectors near the margin
C. Yes - SVMs generally fail on traffic data
D. No - radial basis kernel SVMs can handle this
E. None of the above
5. Employee Count in Python Class
Modified Question.
In a Python Employee class, you want to track how many employee objects have been created using an employeeCount attribute initialized at 0. What's the most appropriate way to increment it inside the __init__ method?
9. Segfault in Boost.Python Application
Modified Question.
You're using boost::python Upon execution, a segmentation fault occurs. Upon execution, a segmentation fault occurs. What's the most likely reason?
- A. Python's Global Interpreter Lock (GIL)
- B. Memory conflict between Python and C++
- C. Returning a C++ string object directly
- D. Improper use of
asyncioin Python - E. Buffer overflow in Python
10. Why Rerun k-means?
Modified Question.
Why is it generally recommended to run the k-means algorithm multiple times with different starting centroids?
- A. Because its objective function is not convex
- B. To prevent numerical instability
- C. To guarantee improving results in each run
- D. To discover different cluster counts
- E. None of the above
11. Grid Search Limitation
Modified Question.
When performing a grid search to find optimal hyperparameters for a model, what's the main drawback of this method?
- A. Optimal value may lie outside the search grid
- B. It can get stuck in a local minimum
- C. It can miss good settings that fall between grid points
- D. It scales exponentially with parameter count
- E. It can't handle floating-point parameters
12. Probability of Having Disease (Bayes' Rule)
Modified Question.
In a population, 2% have a specific condition. A new test has a 97% true positive rate and a 5% false positive rate. If you take the test twice and both are positive, assuming independence, what's the approximate probability you actually have the condition? both are positive, assuming independence, what's the approximate probability you actually have the condition?
- A. 0.94
- B. 0.91
- C. 0.89
- D. 0.97
- E. 0.87
13. Python Scope Resolution Order
Modified Question.
What is the correct order of variable scope resolution in Python?
- A. Local → Enclosing → Global → Built-in
- B. Local → Global → Built-in → Enclosing
- C. Built-in → Global → Local → Enclosing
- D. Built-in → Global → Enclosing → Local
- E. Local → Built-in → Global → Enclosing
14. Unsupervised Anomaly Detection
Modified Question.
Which of the following best reflects how to train an unsupervised anomaly detection system?
- A. Use both normal and anomalous data equally
- B. Use anomalous samples only
- C. Use only normal data
- D. Assume anomaly rate is equal to normal to balance data
- E. A and D
15. Dependency in Bayesian Network
Modified Question.
Given variables A, B, C, D, E with dependencies.
- C depends on A
- B depends on A
- D depends on B, C
- E depends on C
Which of the following is NOT necessarily true?
- A. E depends on C
- B. D is independent of A given B and C
- C. B is independent of C given D
- D. E is independent of A given C
- E. C depends on A
Programhelp real question tutorial case sharing｜Remote and seamless on-line, safe and stable control
Recently we assisted a student from UIUC to complete the Citadel Software Engineer OA, this time we provide a full remote and seamless "background online writing" service, he only needs to keep the page open, log in to the examination system on time, the rest of the work will be done by us.
On the day of the test, our technical team completed a number of preparations in advance: remote desktop connection configuration, environment synchronization verification, question script preparation, network link encryption, etc., to ensure that after entering the OA system, our side can stably read the questions, and real-time solving, writing codes, and submitting tests.
For this Citadel exam, there were two programming questions and one set of math and logic questions. The programming part examines the order matching logic + log reconstruction, which is a typical medium-high difficulty practical question. Our backend completed the modeling and code implementation in the first time after receiving the questions, including core logic, boundary processing, performance optimization, etc. All the codes were written and inputted into the page by our professional engineers on the spot to ensure that the passing rate and code quality are up to standard.
Math and logic questions are the place to fight for rhythm and mental quality, we use a dual-machine linkage strategy: a real-time reading of the question surface, another rapid deduction of the answer and synchronization of the answer, each question is completed in 15~30 seconds, greatly exceeding the normal pace of the candidates.
The whole process we did a real "zero disturbance + zero operation trace + stable delivery". Students only need to test the equipment in advance according to our instructions, and keep the network smooth and the page online on the day of the exam, and leave the rest to us.
The final result was very satisfactory: all programming questions were AC, the math and logic questions were correct up to 95%, the system score was perfect, and I was invited to a follow-up interview with Citadel.
Programhelp reminders
Citadel's OA is not just a competition of algorithms, it is more like a comprehensive test of hard power + rhythm management ability. Many students have no problem writing code, but the rhythm is disorganized, reading the questions is stuck, the mind can not turn over, as usual, brush off. It is recommended to prepare early and simulate the "real test environment" to train the sense of rhythm and anti-pressure.
If you:
- Want to learn about Citadel OA's recent questions?
- Need question templates & high-frequency test summaries
- Wanted Remote Uncensored OA Tutoring / Simulation Training
wellcome Contact Us!
