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"
"Believe me i'm a student here jn US. Recently interviewed for MSFT. They asked me exact question from PracHub. I saw it the night before and ignored it cause why waste time on random sites. I legit wanna go back and redo this whole thing if I had chance. Not saying will work for everyone but there is certainly some merit to that website. And i'm gonna use it in future prep from now on like lc tagged"
"10 years of experience but never worked at a top company. PracHub's senior-level questions helped me break into FAANG at 35. Age is just a number."
"I was skeptical about the 'real questions' claim, so I put it to the test. I searched for the exact question I got grilled on at my last Meta onsite... and it was right there. Word for word."
"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."
Solve probability and expectation problems
You are asked to solve the following probability and mathematical interview problems: 1. Squid Game glass bridge: There are B sequential bridge steps....
Implement a single-producer multi-consumer ring buffer
Implement a fixed-capacity ring buffer in C++ for a setting with one producer and multiple consumers. Design a class that stores integers in a preallo...
Sort a nearly sorted array
Given an array of length \(n\) in which every element is at most \(k\) positions away from its location in the fully sorted order, design an algorithm...
Choose models for trading tasks
You are given several modeling options for quantitative trading or pricing work: linear regression, convolutional neural networks, transformers, and r...
Find earliest common meeting slot
Given K participants' calendars, each a list of busy intervals [start, end) within a working window [workStart, workEnd], and a meeting duration d min...
Merge K timestamped lists with timestamp coalescing
You are given k sorted lists (or linked lists) of records. Each record has: - timestamp (integer) - values (an array of integers sorted in non-decreas...
Design stock price time-series store and query
Problem Design a platform that stores stock prices over time and can be queried later. Core functionalities 1. Ingest price: The system receives event...
Design a token manager with lazy expiration
Problem Design a token manager that tracks authentication tokens with a fixed time-to-live (TTL). Each token is valid in the half-open time interval [...
Return nodes on a tree diameter path
Problem You are given an undirected tree with n nodes labeled 0..n-1 (connected, no cycles). The diameter of a tree is the longest simple path between...
Implement lazy unique-merge generator for sorted streams
Write a Python generator merge_unique(a, b) that lazily merges two nondecreasing iterables a and b (potentially infinite) into a single nondecreasing ...
Determine order of alien alphabet
You are given a list of words sorted in lexicographic order according to an unknown ("alien") alphabet. Task Return one valid ordering of the unique c...
Solve two DS&A optimization problems
Problem 1 — Maximize alternating-sum over four array partitions: Given an integer array arr[1..n] (1-based). Choose indices a, b, c with 1 ≤ a ≤ b ≤ c...
Solve four algorithmic problems
Answer the following independent algorithmic questions: 1) Count extendable prefixes for '10' subsequences: Given a binary string s and an integer k, ...
Stabilize LLM inference and estimate needed repeats
You run an LLM-based sentiment model to score a fixed dataset of texts. Because the inference API doesn’t let you set temperature (and outputs are sto...
Minimize changes for k-periodic palindrome
Question Given a string currentPassword (length N) and an integer k (1 ≤ k < N, N ≤ 2·10^5, lowercase letters, N divisible by k), find the minimum num...
Implement left join on Python lists, no packages
Implement a left join in pure Python (no external packages, no pandas). Input: left = list of dicts with key 'id' and arbitrary other fields; right = ...
Describe current work and relocation willingness
Behavioral Screen: Responsibilities, Project Deep Dive, and Relocation You are interviewing for a Software Engineer role in a behavioral/leadership HR...
Optimize password transform and discount scheduling
Part 1 — Transform to palindromic k-periodic string: Input: a lowercase string currentPassword and integer k. Constraints: 1 <= k < len(currentPasswor...
Match a string with wildcard pattern recursively
Implement a function that checks whether an input string matches a wildcard pattern. Pattern rules - ? matches exactly one character. - * matches any ...
Implement an in-memory order book API
Problem Implement an in-memory limit order book for a single trading symbol. You do not need to implement order matching/execution—only store and main...