Citadel Interview Questions
Practice 79 real interview questions from Citadel. Covers Coding & Algorithms, Statistics & Math, Machine Learning, Behavioral & Leadership. For roles including Data Scientist, Software Engineer, Machine Learning Engineer.
"I got asked a hardcore MCM DP question and I saw it on PracHub as well. Solved that question in 5 minutes. Without PracHub I doubt I could solve it in 5 hours. Though somehow didn't get hired, perhaps I guess I solved it too fast? /s"
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"Got a Google recruiter call on Monday, interview on Friday. Crammed PracHub for 4 days. Passed every round. This platform is a miracle worker."
"I've used LC, Glassdoor, and random Discords. Nothing comes close to the accuracy here. The questions are actually current — that's what got me. Felt like I had a cheat sheet during the interview."
"The solution quality is insane. It covers approach, edge cases, time complexity, follow-ups. Nothing else comes close."
"Legit the only resource you need. TC went from 180k -> 350k. Just memorize the top 50 for your target company and you're golden."
"PracHub Premium for one month cost me the price of two coffees a week. It landed me a $280K+ starting offer."
"Literally just signed a $600k offer. I only had 2 weeks to prep, so I focused entirely on the company-tagged lists here. If you're targeting L5+, don't overthink it."
"Coaches and bootcamp prep courses cost around $200-300 but PracHub Premium is actually less than a Netflix subscription. And it landed me a $178K offer."
"I honestly don't know how you guys gather so many real interview questions. It's almost scary. I walked into my Amazon loop and recognized 3 out of 4 problems from your database."
"Discovered PracHub 10 days before my interview. By day 5, I stopped being nervous. By interview day, I was actually excited to show what I knew."
"I recently cleared Uber interviews (strong hire in the design round) and all the questions were present in prachub."
"The search is what sold me. I typed in a really niche DP problem I got asked last year and it actually came up, full breakdown and everything. These guys are clearly updating it constantly."
Compute BBO and NBBO from order data
You are given a list data of order records. Each record is a 4-tuple: ` (exchange_id, price, quantity, order_type) ` - exchange_id: string/int identif...
Solve probability and stopping questions
Answer the following independent interview questions: 1. Let X and Y be independent random variables, each distributed Uniform(0,1). Find the probabil...
Design dynamic weighted random sampling with updates
Problem: Support weighted random sampling with insert/delete Design a data structure that maintains a dynamic set of items, each with a positive integ...
Analyze Correlations and Generate Gaussians
You are interviewing for a quantitative data science role. Answer the following probability and simulation questions: 1. Let \(X\), \(Y\), and \(Z\) b...
Simulate 2048 and pack board into uint64
Problem: 2048 move simulation + board compression You are implementing part of the 2048 game on a fixed 4×4 grid. Part A — Simulate a move Given a 4×4...
Sort a Nearly Sorted Array
Given an array nums of length n in which every element is at most k positions away from its location in the fully sorted order, return the array in so...
Implement LRU/LFU cache with custom eviction
You are asked to implement an in-memory key-value cache with a fixed capacity. When the cache is full and a new item must be inserted, an eviction pol...
Compute maximum later-earlier difference
You are given an integer array output (length n ≥ 1). Define the gain of choosing indices i < j as output[j] - output[i]. Return the maximum gain over...
Find the Shortest Target-Sum Path
Given the root of a binary tree and an integer targetSum, find a root-to-leaf path whose node values add up to targetSum. Return the path as a list of...
Design a low-latency trading platform
Design the architecture for a high-frequency fixed-income trading system. The platform should ingest live market data from multiple venues, maintain l...
Solve Classic Probability Questions
An onsite interview included the following independent probability and expectation questions: 1. Squid Game bridge problem. In the classic glass-bridg...
Implement task queue with insert, delete, execute
Problem: Task manager with insert/delete/execute-next Design a data structure to manage executable tasks. Each task has: - taskId (unique) - priority ...
Find constant minimizing absolute error
You have a dataset of real-valued targets \(y_1, y_2, \dots, y_n\). You want to fit a constant predictor (no features): - Prediction: \(\hat y_i = c\)...
Determine When a Quadratic Has Finite Minimum
Consider the unconstrained real-valued optimization problem \[ \min_{x \in \mathbb{R}^n} f(x) = x^\top Qx + c^\top x, \] where \(Q \in \mathbb{R}^{n \...
Implement array merge, round-robin scheduler, and trading simulator
You are given three independent coding prompts. For each prompt, clearly define your function/class interfaces, handle edge cases, and analyze time/sp...
Design alerting for application-to-exchange mappings
Problem: Alerting design for application→exchange mappings You are building a service that receives an ordered stream of mapping events: - register(ap...
Design a low-latency trading system
System Design: Low-Latency Electronic Trading Platform (Equities) You are designing a single-region electronic trading platform (exchange/ATS-like) th...
How do you handle conflict at work?
Describe a time you had a conflict with a teammate (e.g., disagreement on technical direction, priorities, code quality, or ownership). Please cover: ...
Estimate constant under absolute loss
Suppose you have observed target values \(y_1, y_2, \dots, y_n\), and you want to fit the simplest possible model that predicts the same constant valu...
Check whether a string is a palindrome
Problem Given a string s consisting only of lowercase English letters (a-z), determine whether s is a palindrome. A palindrome reads the same forward ...