Interview Experiences

Real candidates, real loops: every round, what was asked, and how it ended.

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21 stories

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CitadelSoftware EngineerIntern
Sep 2026

Merging K Timestamped Price Feeds into a Running Price in Technical Round 3

Citadel SWE intern technical interview. The interviewer was from Citadel Securities. Problem description: You are given K data streams (feeds), and each feed is already sorted by timestamp in ascending order. Each event has two fields: a timestamp and a price delta. Requirement: merge the events from all the feeds in time order, and after processing each event, output the current cumulative absol…

Technical Screen0
CitadelSoftware EngineerIntern
Sep 2026

A Deep Dive on the Classic Orderbook Problem

This was my second round for the Citadel SWE intern process. The technical part was the classic orderbook problem. The question was the classic orderbook problem. Problem description: Design and implement an order book data structure that maintains order records containing the exchange name, price, quantity, and side (bid or ask). It needs to support three core APIs: add(exchange, price, quantity…

Technical Screen1
CitadelSoftware EngineerIntern
Sep 2026

File Deduplication, Size Checks, and Reference Counts

My first Citadel SWE interview. The interviewer was on the hedge fund side. I gave a brief introduction. Before I had a chance to tell the behavioral stories I'd prepared, he went straight into technical questions. The interview was basically 100% coding and system design. Problem: Suppose a file system contains files with identical contents. For example, /a/b/c.txt and /a/b/e.txt both contain th…

Technical Screen1
CitadelSoftware Engineer
Aug 2026

A Maddeningly Vague Data Sampling Question

Citadel is out of their minds. The first half was fine — a normal self-introduction, project walkthrough, basic behavioral questions. Then the coding part started and that's where the craziness began: The interviewer was mumbling and couldn't speak clearly, and gave me a purely verbal problem: "we have millions of data points that need to be labeled," and told me to find the useful data. I kept f…

Technical Screen0
CitadelSoftware Engineer
Aug 2026

Optimizing a Correct C++ Function to Run Under 100 Microseconds

The assessment provided C++ source code for a root_node function. Its logic was correct, but it ran extremely slowly. The task was to refactor and optimize it so that it would finish in strictly less than 100 microseconds on large inputs. The original code contained nested loops and operations such as std::find_if and std::advance, producing O(N²) complexity. I needed to reduce that to O(N). It a…

Online Assessment0
CitadelSoftware EngineerIntern
Aug 2026

A Course Schedule Variant That Didn't Quite Run

This was for a 2027 summer internship, interviewing in the summer before my junior year. The first 15 minutes were self-introduction plus resume questions. The resume question was pretty vague — the interviewer only asked one question, but it actually bundled two things together: my most technically challenging experience, and whether I had a feature that directly helped with product commercializ…

Technical Screen0
CitadelSoftware Engineer
Aug 2026

Spreadsheet Coding Round, Rejected for Weak System Design

Sharing my recent first technical round for an experienced-hire role on Treasury Engineering at the Citadel hedge fund. It was in Python and lasted about an hour. For the first 15 minutes or so we talked about my background. They asked whether I prefer research or engineering, what I like most and least about my current job from a technical point of view, and whether I take part in production sup…

RejectedTechnical Screen0
CitadelSoftware Engineer
Jul 2026

Onsite Design Round Interrupted Nonstop by a Confused Interviewer

I just finished interviewing for Citadel Securities' C++ SWE position, and the whole experience was very negative, so I'm posting here to vent. The phone screen was an external merge sort with a heap. The interviewer was decent, and the overall experience was fine. After that, they quickly scheduled the onsite and told me there'd be five rounds total: design + 2h coding + 1h code review + 1h proj…

Onsite0
CitadelSoftware Engineer
Jun 2026

A No-Code, All-Whiteboard Screen with a Quant Developer

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In progressTechnical ScreenPremium0
CitadelSoftware Engineer
May 2026

Two First Rounds and Progressive Matrix Questions

I asked a lot of people, and they all said they had two first-round interviews. I received both as well, but I did not make it to the second round. The first one: I was asked only one question: share some especially difficult problems you worked on recently and explain them. For the coding portion, a prefix tree or trie was enough to solve it. The question was very similar to a search suggestion…

RejectedOnsite0
CitadelData Scientist
Apr 2026

Temperature Models, Interpolation, and Streaming Regression

First question Background You are given daily temperature data for P towns and daily temperature data for New York City over the same N days. Write functions to answer several questions. Part One — five questions Q1: Which place, either one of the towns or New York City, has the greatest temperature variation, measured by standard deviation? Q2: When Town2's temperature is between 90 and 100 degr…

Technical Screen0
CitadelSoftware Engineer
Mar 2026

2027 OA, Two Problems in 75 Minutes

There were two problems, with 75 minutes in total. First problem: Given an initial work schedule for n days, an employee earns a fixed amount for each working day. If the previous day was also a working day, the employee earns an additional bonus. The employee may change at most k days off into working days, but may not change a working day into a day off. The goal is to choose which days off to…

Online Assessment0
CitadelData Scientist
Feb 2026

Interviewer Freezes Mid-Screen, Then Asks Me to Estimate a Constant

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Technical ScreenXP0
CitadelQuantitative Developer
Jan 2026

Four Rounds Then Waitlisted Despite Good Feedback

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RejectedOnsiteXP0
CitadelSoftware Engineer
Jan 2026

Passed Every Technical Round, Then Stuck in Team-Match Purgatory

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WithdrewOnsiteXP0
CitadelData Scientist
Jan 2026

A Late, Awkward Interviewer and One Linear-Fit Question

The technical interview was supposed to be 30 minutes, but the interviewer showed up 5 minutes late. Fine, whatever. Then he introduced himself, and the whole thing was really awkward — he stumbled over his words the entire time, and all he actually said was his name and his job title. Then he just froze there, like maybe he was supposed to say something about the company, but he said nothing at…

Technical Screen0
CitadelSoftware Engineer
Dec 2025

HackerRank OA, Two Coding Problems in 75 Minutes

I did this OA on the HackerRank platform. Two questions, 75 minutes. Q2: You're given n employees' office hours as intervals [startTime[i], endTime[i]]. You need to build a team that includes at least one "core employee" whose working hours overlap with every other member's working hours. Find the maximum number of employees the team can include. For example: Input: startTime = [2, 5, 6, 8], endT…

Online Assessment0
CitadelData Scientist
Oct 2025

Five Rounds of Live Math and Python From Scratch

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Technical ScreenXP0
CitadelData Scientist
Oct 2025

Cold Applied, Wildcard Matching Live Coding, Rejected Next Day

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RejectedTechnical ScreenXP0
CitadelSoftware Engineer
Sep 2025

OA Questions Matched a 1point3acres Compilation

I was tested on the last two of these. My solutions passed all the test cases. All of the questions below are from 1point3acres. Prefix Count of "10" Given a binary string sequence of length n, you can perform the following operation any number of times: append a '0' or '1' to the end of the sequence. After updating the sequence (i.e. appending characters to the end of the original sequence), if…

Online Assessment0

What are interview experiences?

An interview experience is a candidate's own account of a hiring loop — not a question bank entry. It tells you the shape of the process: how many rounds there were, what each round actually tested, how long the gaps between them ran, and what the recruiter said at the end. That context is the part a question list cannot give you.

How to read them

Weight recent write-ups more heavily — interview loops change, often within a year. Read several for the same company and role rather than one: a single account tells you what one interviewer asked, while five tell you what the bar is. Note the outcome badge too, since a rejection write-up usually explains the gap far more precisely than an offer one.

Share your own

Every published experience earns 50 XP, and each of the first 3 likes it receives in a day earns you 10 XP more. Likes must come from established accounts; like-for-like swaps and likes from your own second account are not paid. Write it while the details are fresh — the round order, the exact prompts, and how much time you were given are what the next reader needs.

Share your experience to earn XP