The Citadel interview process for software engineers is an online assessment on HackerRank (two LeetCode medium/hard problems), a 45-minute CoderPad interview mixing algorithms with a few behavioral questions, a superday of three 45-minute technical interviews, a leadership interview with a senior engineer from a specific team, and a final review. Every round tests data structures and algorithms at LeetCode medium to hard level, and candidates say the bar is working, optimal code rather than neat style.
Citadel (the hedge fund) and Citadel Securities (the market maker) recruit engineers and researchers through one pipeline and share interview feedback. Quant research adds a probability and statistics superday, and Citadel Securities’ quant trading track uses probability puzzles and market-making games instead of LeetCode.
Citadel interview process
- Online assessment60-75 min
- CoderPad interview45 min
- Superday3 x 45 min
- Leadership interview45-60 min
- Final review-
| Round | Duration | What it tests |
|---|---|---|
| Online assessment | 60-75 min | HackerRank, usually two LeetCode medium/hard problems with hidden test cases |
| CoderPad interview | 45 min | One or two DSA problems plus about 15 minutes of behavioral questions |
| Superday | 3 x 45 min | Back-to-back coding rounds: DP, graphs, implementation and class design |
| Leadership interview | 45-60 min | A senior engineer for one team: project depth, motivation, sometimes more coding |
| Final review | - | Hiring committee decision; interns may go through project or team matching |
Citadel interview questions with answers
Q: Find the smallest (or longest) substring with no repeated characters.
Use a sliding window with a map from character to its last index. Move the right pointer one step at a time; when the new character was last seen inside the window, jump the left pointer to one past that index. Track the best window length as you go. Each character enters and leaves the window at most once, so it runs in O(n) time and O(k) space for an alphabet of size k. Ask which variant they want: the minimum window that contains every distinct character uses the same two pointers with a count of characters still missing.
Q: Frog Jump: can the frog cross the river given stone positions and jump rules?
Store, for each stone, the set of jump sizes that can land on it. Start with stone 0 and jump size 0. For each stone in order and each size k in its set, try k-1, k and k+1; if a stone exists at position plus that size, add the size to that stone’s set. The answer is whether the last stone’s set is non-empty. With n stones the sets hold at most n sizes, so it is O(n^2) time. Citadel’s version had a twist, so restate the jump rule before coding and adapt the transition, not the whole structure.
Q: Reduce the number of currency transfers needed to settle debts between people.
First collapse every transaction into a net balance per person; anyone at zero drops out. A greedy pass that matches the largest creditor with the largest debtor settles everything in at most n-1 transfers. The true minimum needs a search: it equals n minus the maximum number of disjoint groups whose balances sum to zero, which you can find with backtracking or a bitmask DP over subsets for small n. Mention that the bitmask approach is O(2^n * n), fine for about 20 people.
Q: Parallel Courses: what is the minimum number of semesters to finish all courses?
Build the prerequisite graph, compute in-degrees, and run Kahn’s topological sort level by level: each level is one semester. If you process fewer nodes than there are courses, there is a cycle and the answer is -1. The harder variant caps how many courses you can take per semester; then greedy level order is no longer optimal and you need a bitmask DP over the set of completed courses, which is why a 2025 intern called it a hard version.
Q: Maintain the mean of the last k values in a stream.
Keep a fixed-size queue and a running sum. On each new value, add it to the sum and push it; if the queue holds more than k items, pop the oldest and subtract it. The mean is sum divided by queue size, O(1) per update. For floating point over a long stream, mention drift and either use integers where possible or periodically recompute the sum. A follow-up may ask for a time-based window, which swaps the size check for a timestamp check.
Q: Merge k sorted files that are too large for memory.
Open a buffered reader on each file and push the first record of each into a min-heap keyed by value, tagged with its file index. Pop the smallest, write it to a buffered output, then push the next record from the same file. That is O(N log k) for N records. Discuss buffer sizes, since disk reads dominate, and what happens when k exceeds the number of open file handles: merge in passes of a fixed fan-in.
Q: Four stones are each black or white with unknown split. You draw two without replacement and both are black. What is the chance the next one is black?
It depends on the prior, and saying so is part of the answer. With a uniform prior on the number of black stones (0 to 4), the likelihood of two blacks is B(B-1)/12, giving posterior weights 2, 6 and 12 for B = 2, 3 and 4. The chance the next draw is black is then (6 x 1/2 + 12 x 1) / 20 = 0.75. If each stone is independently black with probability 1/2, the first two draws tell you nothing about the rest, so the answer is 0.5.
Q: Two people arrive at a uniformly random time between 4pm and 5pm and each waits 10 minutes. What is the chance they meet?
Draw the 60 x 60 square of arrival times. They miss each other when the gap exceeds 10 minutes, which is two triangles with legs of 50, total area 2,500. So the chance of meeting is 1 - 2,500/3,600 = 11/36, about 0.31. This one appears on a prep site rather than a verified Citadel report, but the geometric method transfers to other quant screens.
Citadel interview questions by role
| Role | Reported questions and topics |
|---|---|
| SWE intern | Smallest substring with non-repeating characters (Feb 2025 technical round); a Frog Jump DP variant (Feb 2025 superday); “reduce currency transfers” (Oct 2025); counting ways to assign n jobs to m intervals with an adjacency rule (Sep 2025 OA); a trie and heap hybrid (Mar 2026); a harder Parallel Courses variant and a sliding-window mean (Nov 2025). |
| New grad / associate SWE | Same DSA level as interns, plus a leadership interview; an associate SWE in April 2025 did not get past the OA. |
| Experienced SWE | k-way merge of disk files with a min-heap; C++ internals (iterators, memory, std::variant, std::vector); OS and networking in team matching. |
| Quant researcher | Probability, statistics and modelling; a London candidate in November 2025 was asked how Y moves if X rises two basis points, given two correlated series. |
| Quant trader (Citadel Securities) | Probability OA, Fermi estimates, dice and coin problems, market making; an October 2025 superday asked the stones-in-a-bag question. |
Citadel SWE intern interview
Citadel’s US software engineer intern posting (removed March 2026) listed Chicago as the main location with roles also in Houston, Miami and New York, an 11-week program and a base of $4,300 to $4,800 per week. It asked for a degree in progress in computer science or a related field, “exceptional programming and design skills” and familiarity with probability and statistics.
The Citadel SWE intern interview usually runs OA, one technical round, a superday of three technical interviews, then team or project matching. An August 2024 New York intern who accepted an offer had:
- A 66-minute HackerRank OA with two LeetCode medium/hard problems.
- A 45-minute phone interview: about 15 minutes of behavioral questions, 30 minutes of coding.
- A superday of three back-to-back technical rounds, mostly LeetCode medium or easier hard, focused on implementation and class design.
- Team matching, where hiring managers chose whether to interview the candidate. It was unstandardized and included one behavioral and one “very challenging” technical interview.
The same candidate said optimal solutions and running, tested code mattered most and code style mattered less. Several 2025 intern candidates were cut at the first technical round, which is a single LeetCode medium after a short resume chat.
Citadel new grad and experienced software engineer interviews
Citadel’s 2025 university graduate software engineer posting listed Miami, Chicago and New York and a base salary of $200,000 to $250,000, plus a discretionary incentive program. The requirements matched the intern posting: strong programming and design, analytical skills, and probability and statistics.
Citadel Securities’ published engineering guide for interns and new grads, as summarized by Quantt, has four steps: a 45-minute CoderPad interview on data structures, algorithms, problem-solving and behavioral questions; three 45-minute interviews, with next steps promised within two weeks and no team-fit assessment; a leadership interview with a senior engineer for a specific team; and a final review. It puts the process at about eight weeks. Neither firm’s guide lists an online assessment, but candidates on several tracks report one.
Experienced hires get more language depth. An April 2026 experienced candidate reported a k-way merge of disk files using a min-heap, and C++ candidates have been asked about iterators, memory management, std::variant and std::vector.
Citadel online assessment: quick answers
| Question | Answer |
|---|---|
| Which platform? | HackerRank, sent automatically after you apply in several 2025 reports. |
| How many problems and how long? | Usually two problems. A 2024 New York intern had 66 minutes. |
| How hard is it? | Reports split. An April 2025 associate SWE called it very difficult and said a perfect score was needed; a September 2025 intern found it LeetCode easy-to-medium. |
| Do partial scores pass? | Sometimes. A February 2025 New York intern advanced with 9/15 test cases on one problem and 5/15 on the other. |
| How soon does it arrive? | About two days after applying in a September 2025 report; that candidate was rejected a week after submitting. |
| Topics reported | Graphs, dynamic programming, counting and scheduling problems. |
Citadel CoderPad screen and superday
The first live round is 45 minutes on CoderPad. In the 2024 offer report it opened with about 15 minutes of behavioral questions (why Citadel, what you want to do next summer) and then 30 minutes of coding. A November 2025 US intern described the same shape: introduction, resume questions, then one LeetCode medium.
The superday is three back-to-back 45-minute coding interviews. Candidates describe LeetCode medium and hard problems, dynamic programming, and implementation or class-design tasks. Interviewers expect you to reach the optimal approach and run your code against tests, so leave time to trace edge cases rather than polishing names.
Citadel quantitative research interview
Citadel Securities’ quant research guide, as summarized by Quantt, starts with a 45-60 minute remote video interview covering programming, research ability, data structures, algorithms and problem-solving, with a CoderPad link sent beforehand. Python and C++ are the core languages, though the firm says any language is welcome. A superday of three to five 60-minute interviews follows, and the process takes about four to five weeks.
Questions lean on statistics and modelling as much as puzzles. The November 2025 London prompt about two correlated series is a regression question: estimate the slope of changes in Y on changes in X, then explain whether the relationship is stable, lagged or spurious.
Citadel Securities quant trading interview
Citadel Securities does not publish its trading process, and candidates say it is not standardized. Reports describe a mostly-probability online test (one 2023 thread described 15 easy probability questions in 30 minutes), a 45-minute first round of Fermi estimates, market making and dice or coin problems, then a superday described as “more market-making.” A Sydney candidate in March 2025 had two technical interviews on probability and game theory. The timeline ranges from under a month to over two months.
Who does well in Citadel interviews
Good fit: You can reach the optimal solution to a LeetCode medium in 20 minutes and still have time to test it, and you are comfortable with DP and graph problems under a timer. For quant research, you can move between a probability derivation and a few lines of Python that check it.
Harder path: You rely on partial credit or on talking through an approach without finishing it. Citadel reports repeatedly mention optimal, running code, and the OA is auto-graded on hidden test cases. Candidates who have never studied operating systems or networking can also struggle in team matching.
A four-week Citadel prep plan
- Week 1: Two timed 66-minute sets of two LeetCode medium/hard problems on HackerRank, one heavy on graphs, one on DP. Note which hidden-case failures came from edge cases you never tested.
- Week 2: Superday simulation: three 45-minute problems back to back, including one class-design or implementation task (an LRU cache, an order book, a rate tracker). Run every solution against your own tests before calling it done.
- Week 3: Fundamentals for team matching: process vs thread, virtual memory, TCP vs UDP, what happens on a cache miss. C++ candidates review iterator invalidation, move semantics and std::variant.
- Week 4: One project you can explain in depth for the leadership interview, a 60-second answer to “why Citadel,” and a mock 45-minute CoderPad round that opens with 15 minutes of behavioral questions.
Quant research track: swap week 2 for probability (conditional probability, expectation, Markov chains) and simple regression, and code a quick simulation for each answer.
Citadel pay in the US
Citadel’s 2025 university graduate software engineer posting (Miami, Chicago, New York) listed a base of $200,000 to $250,000, and its US software engineer intern posting listed $4,300 to $4,800 per week for an 11-week program. Both add a discretionary incentive program and benefits.
For Citadel Securities, TraderMath’s September 2026 review of job ads lists $235,000 to $300,000 base for graduate software engineers and PhD researchers and $4,500 to $5,800 per week for interns. Its summary of US salary filings from July 2025 to June 2026 shows a median filed range of $175,000 to $255,000 for the “Software Engineer” title at Citadel Securities. Bonuses are on top and not published.
Frequently asked questions about Citadel interviews
What is the Citadel interview process for software engineers?
Most campus candidates take a HackerRank online assessment, then a 45-minute CoderPad interview on data structures, algorithms and a few behavioral questions, then a superday of three 45-minute technical interviews, then a leadership interview with a senior engineer for a specific team, then a final review. Citadel Securities’ published engineering guide puts the whole process at about eight weeks.
What is the Citadel SWE intern interview like?
An August 2024 New York intern who got an offer had a 66-minute HackerRank OA with two LeetCode medium/hard problems, a 45-minute phone interview (about 15 minutes behavioral and 30 minutes coding), a superday of three back-to-back technical rounds, and team matching with one behavioral and one hard technical interview. Optimal, running code mattered more than style. Citadel’s intern posting paid $4,300-$4,800 per week for an 11-week program.
How hard is the Citadel online assessment?
Reports disagree. An April 2025 US associate software engineer called the HackerRank OA very difficult compared with other companies and said a perfect score was needed to advance, while a September 2025 New York intern found it relatively easy with LeetCode easy-to-medium problems. A February 2025 New York intern passed with 9 of 15 test cases on one problem and 5 of 15 on the other.
What are common Citadel interview questions?
Reported coding questions include the smallest substring with non-repeating characters, a Frog Jump dynamic programming variant, reducing currency transfers between people, a trie and heap hybrid, a harder Parallel Courses variant, a sliding-window mean, and a k-way merge of disk files with a min-heap. C++ candidates were asked about iterators, memory management, std::variant and std::vector.
Are Citadel and Citadel Securities the same company?
No. Citadel is a hedge fund and Citadel Securities is a market maker. Both were founded by Ken Griffin and remain legally distinct, but for engineering and research they recruit together and both firms review the same interview feedback. Their trading tracks differ: Citadel Securities quant trading uses probability and market-making games.
What is the Citadel quantitative research interview process?
Citadel Securities’ published quant research guide describes a 45-60 minute remote video interview on programming, research ability, data structures, algorithms and problem-solving, with a CoderPad link sent in advance, followed by a superday of three to five 60-minute interviews. Python and C++ are the core languages. The process takes about four to five weeks.
How much does Citadel pay software engineers?
Citadel’s 2025 university graduate software engineer posting for Miami, Chicago and New York listed a base salary of $200,000 to $250,000 plus a discretionary incentive program. Its intern posting listed $4,300 to $4,800 per week. Citadel Securities’ graduate engineer ads list $235,000 to $300,000 base, according to TraderMath’s September 2026 review of its ads.
How long does the Citadel hiring process take?
Citadel Securities’ engineering guide says about eight weeks, with next steps promised within two weeks of the three-interview round. In an October 2025 New York intern report, the first technical round came a few days after the OA and the superday invitation about two weeks later.
What is in the Citadel leadership interview?
It is a conversation with a senior engineer for a specific team after the technical rounds. An October 2025 candidate described it as a mix of technical and behavioral questions spread over two or more calls, and said that was where they were rejected. Expect a deep look at one project, why Citadel, and what you want to work on.
Citadel vs Citadel Securities: which one are you interviewing with?
Citadel was founded in Chicago in 1990 and moved its headquarters to Miami in 2022. Citadel Securities is a separate, legally distinct market maker owned by the same founder, Ken Griffin. For software engineering and quant research the two firms recruit together, so a candidate in one pipeline is effectively talking to both, and both review the same feedback.
The difference shows up after the superday. A February 2025 New York intern said project matching covered operating systems and networking concepts plus LeetCode problems, and that it differed between the Citadel (CIT) and Citadel Securities (CITSec) tracks. On the trading side, Citadel Securities runs probability and market-making interviews, while the hedge fund’s investing seats use stock pitches and modelling cases.
Sources
- Citadel: Software Engineer - 2025 University Graduate (US) posting on Built In
- Citadel: Software Engineer - Intern (US) posting on Built In Chicago
- Quantt: Citadel and Citadel Securities interview process, summarizing the firms’ published guides
- TraderMath: Citadel Securities salaries from job ads and filings
- Wikipedia: Citadel LLC
- Taro: SWE intern, New York, August 2024 (offer)
- Taro: SWE intern, New York, February 2025
- Taro: associate software engineer, United States, April 2025
- Taro: SWE intern, New York, September 2025
- Taro: SWE intern, New York, October 2025
- Taro: SWE intern, United States, November 2025
- Leadership interview description: an October 2025 Glassdoor review of a Citadel software engineering loop