Citadel interview questions

Showing 61–90 of 90 results

• Implement array merge, round-robin scheduler, and trading simulatorMedium

  This problem tests your ability to manipulate data structures efficiently, implement a fair process scheduler, and manage event-driven state transitions.

  CitadelSoftware EngineerCoding & AlgorithmsOnsite
• Implement lazy unique-merge generator for sorted streamsMedium

  This question evaluates knowledge of lazy evaluation, Python generators/iterators, merging nondecreasing streams with duplicate elimination, and considerations of time and space complexity in streaming contexts.

  CitadelData ScientistCoding & AlgorithmsTechnical Screen
• Implement task queue with insert, delete, executeMedium

  This question evaluates a candidate's ability to design and implement efficient dynamic priority management, including priority ordering, insertion-order tie-breaking, and support for add, remove, and execute operations.

  CitadelSoftware EngineerCoding & AlgorithmsOnsite
• Implement two-pointer unique-pair sum searchMedium

  Implement two-pointer unique-pair sum search evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

  CitadelData ScientistCoding & AlgorithmsTechnical Screen
• In-Memory Spreadsheet with Formulas, Cycle Detection and Read vs Write ComputationMedium

  Implement a simplified in-memory spreadsheet in Python with set_cell, set_formula and get_cell, where formulas use the four arithmetic operators and may reference other formula cells. Follow-ups test circular-reference detection, legal repeated references, and the trade-offs of computing values on read versus on write, including caching and invalidation.

  CitadelSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• Make a hard MoE router differentiableHard

  Make a hard MoE router differentiable evaluates core ML concepts, assumptions, math intuition, training/evaluation trade-offs, and practical failure modes in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

  CitadelMachine Learning EngineerMachine LearningTechnical Screen
• Match a string with wildcard pattern recursivelyMedium

  This problem tests your ability to implement a recursive pattern-matching algorithm that handles specific wildcard characters while managing overlapping subproblems.

  CitadelData ScientistCoding & AlgorithmsTechnical Screen
• Maximize Earnings by Adding Working DaysMedium

  Maximize schedule earnings by changing at most k days off into working days, balancing fixed daily pay with bonuses for consecutive working days.

  CitadelSoftware EngineerCoding & AlgorithmsTechnical Screen
• Maximize Earnings by Converting Days OffMedium

  Tests dynamic programming and state tracking to maximize daily earnings and consecutive work streak bonuses under a budget of schedule changes.

  CitadelSoftware EngineerCoding & AlgorithmsHR Screen
• Merge K Drone Telemetry Streams Into a Running Altitude TimelineMedium

  Interleave K drones' individually time-ordered altitude logs into a single replay and track the fleet's shared altitude total as each logged change is applied. Tests k-way merging with a heap, a deterministic tie-break across drones, and correct handling of negative deltas and drones with no events.

  CitadelSoftware EngineerCoding & AlgorithmsTechnical Screen
• Merge K Timestamp-Sorted Price Feeds into a Running Absolute PriceMedium

  Merge K price-event feeds, each already sorted by timestamp, into one chronological stream and return the running absolute price after every event, starting from zero. It tests merging sorted sequences efficiently, a deterministic tie-break for equal timestamps by feed index and then in-feed order, negative deltas, empty feeds, and 64-bit accumulation.

  CitadelSoftware EngineerCoding & AlgorithmsTechnical Screen
• Merge K timestamped lists with timestamp coalescingMedium

  This problem tests your ability to efficiently merge multiple sorted streams of data and aggregate values associated with the same timestamp.

  CitadelSoftware EngineerCoding & AlgorithmsTechnical Screen
• Minimize Changes to Make Every Password Block PalindromicMedium

  Tests string manipulation and two-pointer techniques to determine the minimum character replacements needed to make independent fixed-length blocks palindromic.

  CitadelSoftware EngineerCoding & AlgorithmsHR Screen
• Minimize changes for k-periodic palindromeMedium

  This question evaluates understanding of string algorithms and combinatorial reasoning, focusing on palindrome properties combined with k-periodicity and the ability to minimize character changes under global constraints.

  CitadelSoftware EngineerCoding & AlgorithmsOnline Assessment
• Minimize image processing cost with discountMedium

  This question evaluates a candidate's competence in algorithm design and optimization, including interval-based cost aggregation and modular arithmetic for large-number results within the Coding & Algorithms domain.

  CitadelSoftware EngineerCoding & AlgorithmsOnline Assessment
• Order Book With Per-Exchange BBO and Cross-Exchange NBBO QueriesMedium

  Design and implement an in-memory order book that aggregates quantity by exchange, side and price, and answers per-exchange best bid and offer and cross-exchange NBBO queries. It tests heap ordering with lazy deletion, keeping the global view consistent when any exchange's best price moves, and precise amortized complexity analysis.

  CitadelSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• Perform an External Merge Sort with a HeapMedium

  Implement an external merge sort simulation that partitions a data stream into memory-bounded sorted runs and merges them using a min-heap.

  CitadelSoftware EngineerCoding & AlgorithmsOnsite
• Read and Write Files with Shared ContentEasy

  Design an in-memory file system that shares identical content payloads across multiple file paths to save memory, supporting reads, writes, and deduplication tracking.

  CitadelSoftware EngineerCoding & AlgorithmsTechnical Screen
• Refactor a Correct but Quadratic C++ Routine Under a Microsecond BudgetMedium

  Optimize an inefficient, quadratic tree-resolution routine into a linear-time, cache-friendly implementation suitable for ultra-low-latency execution.

  CitadelSoftware EngineerSoftware Engineering FundamentalsOnline Assessment
• Return a Valid Dependency Order for Named TasksMedium

  Implement a deterministic topological sort for a directed acyclic graph of named tasks with cycle detection and lexicographical tie-breaking.

  CitadelSoftware EngineerCoding & AlgorithmsTechnical Screen
• Return nodes on a tree diameter pathMedium

  This problem tests your ability to perform a two-pass Breadth-First Search (BFS) or Depth-First Search (DFS) on an undirected tree to find the longest path and reconstruct the sequence of nodes that form it.

  CitadelSoftware EngineerCoding & AlgorithmsTechnical Screen
• Simulate 2048 and pack board into uint64Medium

  This question evaluates proficiency in implementing deterministic game-state logic and compact binary representations, specifically array manipulation and merge semantics for 2048 slide operations plus bit-level packing/unpacking of 4-bit exponent fields.

  CitadelSoftware EngineerCoding & AlgorithmsOnsite
• Solve Classic Probability QuestionsHard

  This problem tests your ability to calculate the expected stopping time of a stochastic process and your proficiency with the linearity of expectation in the context of sequential probability.

  CitadelData ScientistStatistics & MathOnsite
• Solve Five Core Python Data-Processing ExercisesMedium

  Implement and explain: repeat a message `n` times with blank lines; square a list then reverse it; FizzBuzz; count case-sensitive words; and return the second-largest unique integer or `None`. Make the API or object boundaries explicit, then cover invariants, edge cases, testing strategy, and operational trade-offs.

  CitadelSite Reliability EngineerSoftware Engineering FundamentalsTechnical Screen
• Solve probability and expectation problemsHard

  This set of problems evaluates probabilistic reasoning and expectation skills across discrete and continuous settings, covering conditional probability with evolving information, convolution and distribution derivation, occupancy/collector problems, symmetry-based variance on manifolds, and sequential selection/optimal stopping.

  CitadelData ScientistStatistics & MathOnsite
• Sort a nearly sorted arrayHard

  This question evaluates algorithmic problem-solving skills, specifically understanding sorting under constrained inputs and rigorous time and space complexity analysis.

  CitadelData ScientistCoding & AlgorithmsOnsite
• Stabilize LLM inference and estimate needed repeatsMedium

  This question tests the ability to design an LLM inference pipeline that ensures result stability through statistical aggregation and estimates the minimum number of inference samples required to achieve a target confidence level.

  CitadelData ScientistML System DesignTechnical Screen
• Top-K Largest Elements in Every Sliding WindowMedium

  Design an algorithm to maintain and extract the top-K largest elements in descending order for each sliding window of size W across an array.

  CitadelSoftware EngineerCoding & AlgorithmsTechnical Screen
• Two-Player Terminal Battleship: Ship Placement From Input, Then Turn-Based AttacksMedium

  Build a two-player Battleship game as a class that runs in the terminal, with players taking turns to place ships by typing coordinates and sizes, then extend it so they can attack each other's fleets. It tests object modeling, input parsing and validation, turn handling, and delivering a large amount of working code under time pressure.

  CitadelSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• Update No-Intercept Regression Slopes Across BatchesMedium

  Compute cumulative no-intercept regression slopes as paired data arrives in batches. Reuse running cross-products and sums of squares instead of refitting all historical rows.

  CitadelData ScientistCoding & AlgorithmsTechnical Screen