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Interview Questions
Practice 9403 coding, system design and machine learning questions from 546 companies, sorted by role, topic and interview round. Every question has step-by-step hints, a code runner that supports 8 languages and an AI mentor; members also get the full solution walkthrough.
- 9403
- Questions
- 546
- Companies
- 11
- Topics
- 8
- Languages
Showing 1171–1200 of 4616 results
- CitadelEasySoftware EngineerImplement LRU/LFU cache with custom eviction
This problem tests your ability to design a generic cache structure that supports interchangeable eviction strategies, requiring efficient lookup and metadata management.
Coding & AlgorithmsTechnical ScreenHash MapLinked ListCache - CitadelMediumData ScientistImplement Piecewise Linear Interpolation and Extrapolation
Implement piecewise linear interpolation from unsorted knots, including exact-knot behavior and endpoint extrapolation. Practice paired sorting, binary search, and numerical edge cases.
Coding & AlgorithmsTechnical Screen - CitadelMediumSoftware EngineerImplement a single-producer multi-consumer ring buffer
This question evaluates understanding of ring-buffer data structures, circular indexing, fixed-capacity storage, and object-oriented design for a single-producer, multi-consumer implementation in C++.
Coding & AlgorithmsTechnical Screen - CitadelEasySoftware EngineerImplement an in-memory order book API
This problem tests your ability to design an in-memory data structure for an order book using efficient data structures to support order management and price-level aggregation.
Coding & AlgorithmsTechnical ScreenData StructuresHash MapTree - CitadelMediumData ScientistImplement lazy unique-merge generator for sorted streams
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.
Coding & AlgorithmsTechnical Screen - CitadelMediumData ScientistImplement two-pointer unique-pair sum search
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.
Coding & AlgorithmsTechnical Screen - CitadelMediumSoftware EngineerIn-Memory Spreadsheet with Formulas, Cycle Detection and Read vs Write Computation
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.
Software Engineering FundamentalsTechnical Screen - CitadelHardMachine Learning EngineerMake a hard MoE router differentiable
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.
Machine LearningTechnical Screen - CitadelMediumData ScientistMatch a string with wildcard pattern recursively
This problem tests your ability to implement a recursive pattern-matching algorithm that handles specific wildcard characters while managing overlapping subproblems.
Coding & AlgorithmsTechnical ScreenRecursionDynamic ProgrammingString Matching - CitadelMediumSoftware EngineerMaximize Earnings by Adding Working Days
Maximize schedule earnings by changing at most k days off into working days, balancing fixed daily pay with bonuses for consecutive working days.
Coding & AlgorithmsTechnical Screen - CitadelMediumSoftware EngineerMerge K Drone Telemetry Streams Into a Running Altitude Timeline
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.
Coding & AlgorithmsTechnical Screenheapmerge-intervalsstreaming - CitadelMediumSoftware EngineerMerge K Timestamp-Sorted Price Feeds into a Running Absolute Price
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.
Coding & AlgorithmsTechnical Screen - CitadelMediumSoftware EngineerMerge K timestamped lists with timestamp coalescing
This problem tests your ability to efficiently merge multiple sorted streams of data and aggregate values associated with the same timestamp.
Coding & AlgorithmsTechnical ScreenHeapMerge SortData Streams - CitadelMediumSoftware EngineerOrder Book With Per-Exchange BBO and Cross-Exchange NBBO Queries
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.
Software Engineering FundamentalsTechnical Screen - CitadelEasySoftware EngineerRead and Write Files with Shared Content
Design an in-memory file system that shares identical content payloads across multiple file paths to save memory, supporting reads, writes, and deduplication tracking.
Coding & AlgorithmsTechnical ScreenHash TableDesignString - CitadelMediumSoftware EngineerReturn a Valid Dependency Order for Named Tasks
Implement a deterministic topological sort for a directed acyclic graph of named tasks with cycle detection and lexicographical tie-breaking.
Coding & AlgorithmsTechnical ScreenGraphTopological SortHeap - CitadelMediumSoftware EngineerReturn nodes on a tree diameter path
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.
Coding & AlgorithmsTechnical ScreenTreesGraph TheoryBFS - CitadelMediumSite Reliability EngineerSolve Five Core Python Data-Processing Exercises
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.
Software Engineering FundamentalsTechnical Screen - CitadelMediumData ScientistStabilize LLM inference and estimate needed repeats
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.
ML System DesignTechnical ScreenLLMInferenceStatistics - CitadelMediumSoftware EngineerTop-K Largest Elements in Every Sliding Window
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.
Coding & AlgorithmsTechnical ScreenSliding WindowHeapOrdered Set - CitadelMediumSoftware EngineerTwo-Player Terminal Battleship: Ship Placement From Input, Then Turn-Based Attacks
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.
Software Engineering FundamentalsTechnical Screen - CitadelMediumData ScientistUpdate No-Intercept Regression Slopes Across Batches
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.
Coding & AlgorithmsTechnical Screen - Citadel SecuritiesMediumSoftware EngineerDefine a Reliable Trade-Reconciliation Library Contract
Define trade-reconciliation contracts and OOP boundaries with exact values, timestamp tolerance, partial-fill questions, deterministic policy ownership, and traceable breaks.
Software Engineering FundamentalsTechnical Screen - Citadel SecuritiesMediumSoftware EngineerDesign a Top-Ten Trade Query with Exact Amounts
Design a top-ten trade query around an explicit ranking contract, exact monetary aggregation, bounded heaps, timestamp boundaries, and mutable-score streaming tradeoffs.
Software Engineering FundamentalsTechnical Screen - ClickhouseMediumData EngineerAnswer SQL And Data Warehouse Fundamentals For A Data Engineering Interview
This problem tests foundational knowledge of SQL set operations, performance optimization techniques for join operations, and the architectural principles behind building scalable data warehouses.
Data Manipulation (SQL/Python)Technical ScreenSQLData WarehousingWindow Functions - CloudKitchensMediumSoftware EngineerAnswer static and streaming Top-K queries
This question evaluates understanding of frequency counting, top-K selection, streaming and sliding-window algorithms and data-structure design in the Coding & Algorithms domain, testing both conceptual algorithmic reasoning and practical implementation skills.
Coding & AlgorithmsTechnical Screen - CloudKitchensMediumSoftware EngineerDesign a menu manager with enums
This question evaluates data modeling with enums, efficient data structure selection to meet specified time complexities, API design for CRUD operations, and practical implementation skills including a command-line interface and unit testing.
Coding & AlgorithmsTechnical Screen - CloudKitchensMediumSoftware EngineerDesign an in-memory cloud storage system
This problem tests your ability to design an efficient in-memory storage manager that handles concurrent file operations, user-based quotas, and data eviction policies.
Coding & AlgorithmsTechnical ScreenData StructuresSystem DesignOptimization - CloudKitchensMediumSoftware EngineerDesign receipt system with combo discounts
A CloudKitchens software-engineer technical screen: build a point-of-sale order that prints an itemized receipt on every item tap, then extend it to apply combo discounts. It tests cart data-structure design, receipt formatting, and the algorithm for selecting a valid set of non-overlapping combos.
Coding & AlgorithmsTechnical Screen - CloudKitchensMediumSoftware EngineerImplement concurrent order-accept/pickup simulator
This question evaluates concurrency and synchronization skills, including thread-safe design, inter-thread communication, state tracking, and correctness properties such as race-condition avoidance and deadlock freedom.
Coding & AlgorithmsTechnical Screen
Citadel
Citadel Securities