Citadel Online Assessment (OA) Questions

Q: How many OA questions does Citadel ask?

AceOffer has reconstructed 18 distinct Citadel OA interview questions from 46 verified candidate reports, each with verbatim follow-ups and a last-reported date.

Q: What is the most common Citadel OA interview question?

NXT OA Multiple-Choice Topics (OS, Systems, Complexity) — reported 6 times, last seen September 2026.

Q: When does Citadel send its online assessment?

The Citadel OA reports AceOffer has run from January 2025 to September 2026; the most recent is from September 2026. Timing within a hiring cycle varies by role, so check each question page for its own dates.

Q: Which platform does Citadel use for the OA?

1 of the 18 Citadel OA question pages mentions HackerRank, from candidate reports. Other reports do not name the platform.

Q: How long is the Citadel OA?

Reports mention time limits from 75 to 120 minutes, depending on the assessment. Each question page notes its own timing where candidates reported it.

Q: How fresh is AceOffer's Citadel OA question data?

The catalog is refreshed monthly from new candidate reports, and every question shows when it was last reported.

These are the 18 online assessment (OA) questions Citadel candidates reported receiving, sorted by how often each was reported, and all of them are free to read. NXT OA Multiple-Choice Topics (OS, Systems, Complexity) leads at 6×. Every question shows when it was last reported; the catalog refreshes monthly.

Part of the full catalog of Citadel interview questions, covering every round.

Key facts

•18 distinct OA questions indexed
•46 candidate reports across those questions
•Most reported: NXT OA Multiple-Choice Topics (OS, Systems, Complexity) — 6× (last seen September 2026)
•All 18 free to read, no account needed
•OA reports span January 2025 – September 2026
•1 of 18 question pages mentions HackerRank
•Time limits mentioned: 75–120 minutes
•Refreshed monthly · last updated October 2026

Which Citadel rounds ask OA questions?

The Citadel rounds below are where these questions come up. Counts are distinct questions, not times asked.

Campus intern and new-grad loops: two coding problems in 75 minutes on HackerRank. The k-periodic palindrome, the four-way array split, the hackathon team, the prefix/suffix match score and distinct palindromic substrings recur. NXT and backend loops: eight to fifteen multiple-choice questions on caching, locks, message queues, proxies, complexity and debugging, plus coding, most often the earliest free meeting slot; the two most recent reports list two coding problems.18 questions

Most reported: NXT OA Multiple-Choice Topics (OS, Systems, Complexity) — 6×

Which Citadel OA questions get asked most?

Sorted by candidate-report frequency. Click any question for the full breakdown.

Question	Round	Reported	Last seen
NXT OA Multiple-Choice Topics (OS, Systems, Complexity)Free The Citadel NXT online assessment (90 to 120 minutes) starts with multiple-choice questions, 8, 14, about 15 or a dozen or so…	OA	6×	September 2026
Earliest Free Meeting Slot from Event StringsFree You are given a list of n event strings, events, and an integer k, the length of a meeting in minutes. Each…	OA	5×	August 2025
Count (Distinct) Palindromic Substrings (LC 647 variant)Free A palindrome is a string that reads the same forwards and backwards, such as 121 or tacocat. A substring is a contiguous…	OA	5×	June 2026
Best Substring by Prefix/Suffix Match ScoreFree Given three strings, text, prefixString and suffixString, score the substrings of text: - prefixScore: the length of the longest substring of text…	OA	3×	March 2025
Tree Diameter Endpoints via Double BFS (LC 1245-style)Free Online assessment, problem 3 of 3. Citadel's 90-minute HackerRank assessment (three coding problems) ends with a tree problem. Three candidates reported it:…	OA	3×	June 2026
Min Changes to Make Password a K-Periodic PalindromeFree Two problems in 75 minutes, online assessment. This is one of them. You are given a string currentPassword and an integer k.…	OA	3×	September 2025
Token Expiry and Reset Simulation (LC 1797-style)Free Authentication tokens. After a user logs in they receive a token. The token expires once the system's time limit, expiryLimit, has passed;…	OA	3×	June 2026
Best Downward Path Sum in a TreeFree Given a tree with n nodes, rooted at node 0 (nodes are numbered 0 to n-1), where values[i] is the value of…	OA	2×	April 2025
Optimise root_node() C++ from O(N²) to O(N)Free You are given a C++ function, root_node, that the task describes as correct but slow. Refactor it and speed it up: work…	OA	2×	September 2026
Prefixes Extendable to Exactly K '10' SubsequencesFree Given a binary string sequence and an integer k, you may append any number of characters, each '0' or '1', to the…	OA	2×	September 2025
Friend Recommendation by Most Common FriendsFree There are n users indexed 0 to n - 1, and m friendships given as a 2D array friendships, where each entry…	OA	2×	April 2025
Count Process Schedules with No Consecutive RepeatsFree Assign processes to time intervals so that no process runs in two consecutive intervals, and count the valid assignments. The fuller of…	OA	2×	December 2025
Max Gross Value of a Four-Way Array SplitFree Given an array arr of n integers, a triplet of 1-based indices i1, i2, i3 with 1 ≤ i1 ≤ i2 ≤…	OA	2×	September 2025
Largest Hackathon Team Under Skill-Rank ConstraintsFree There are n developers, and the skill level of the i-th developer is i, for 1 ≤ i ≤ n. The task…	OA	2×	October 2025
Largest Team with a Core Employee OverlapFree Form the largest team of employees such that at least one member, the core employee, has office hours that overlap the hours…	OA	1×	December 2025
Source Key-Value Override in First-Seen Order (NXT OA)Free Online assessment (NXT Engineering Test): the first of two coding problems. You are given sources, a 2D array of strings. Each row…	OA	1×	October 2025
All Achievable MEX Values After Increment OperationsFree There are n memory blocks, and the size of the i-th block is memoryBlocks[i] (0 ≤ i < n). The operation: select…	OA	1×	October 2025
Min Cost Image Processing with Daily Discount (OA)Free Reported by a Citadel Software Engineer intern (US) candidate as the second of two problems in a 75-minute round. Input: an integer…	OA	1×	July 2025

Browse the full Citadel catalog →

FAQ

How many OA questions does Citadel ask?▾

AceOffer has reconstructed 18 distinct Citadel OA interview questions from 46 verified candidate reports, each with verbatim follow-ups and a last-reported date.

What is the most common Citadel OA interview question?▾

NXT OA Multiple-Choice Topics (OS, Systems, Complexity) — reported 6 times, last seen September 2026.

When does Citadel send its online assessment?▾

The Citadel OA reports AceOffer has run from January 2025 to September 2026; the most recent is from September 2026. Timing within a hiring cycle varies by role, so check each question page for its own dates.

Which platform does Citadel use for the OA?▾

1 of the 18 Citadel OA question pages mentions HackerRank, from candidate reports. Other reports do not name the platform.

How long is the Citadel OA?▾

Reports mention time limits from 75 to 120 minutes, depending on the assessment. Each question page notes its own timing where candidates reported it.

How fresh is AceOffer's Citadel OA question data?▾

The catalog is refreshed monthly from new candidate reports, and every question shows when it was last reported.

Get the full Citadel catalog

Every question, every candidate-reported follow-up, and what passers actually do. Monthly refresh.

See pricing ← All Citadel interview questions