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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
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- 11
- Topics
- 8
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Showing 2341–2370 of 9403 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 - CitadelMediumSoftware EngineerImplement array merge, round-robin scheduler, and trading simulator
This problem tests your ability to manipulate data structures efficiently, implement a fair process scheduler, and manage event-driven state transitions.
Coding & AlgorithmsOnsiteArraysQueuesHeaps - 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 - CitadelMediumSoftware EngineerImplement task queue with insert, delete, execute
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.
Coding & AlgorithmsOnsite - 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 EngineerMaximize Earnings by Converting Days Off
Tests dynamic programming and state tracking to maximize daily earnings and consecutive work streak bonuses under a budget of schedule changes.
Coding & AlgorithmsHR Screendynamic-programmingalgorithmssliding-window - 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 EngineerMinimize Changes to Make Every Password Block Palindromic
Tests string manipulation and two-pointer techniques to determine the minimum character replacements needed to make independent fixed-length blocks palindromic.
Coding & AlgorithmsHR Screenstringstwo-pointersgreedy - CitadelMediumSoftware EngineerMinimize changes for k-periodic palindrome
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.
Coding & AlgorithmsOnline Assessment - CitadelMediumSoftware EngineerMinimize image processing cost with discount
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.
Coding & AlgorithmsOnline Assessment - 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 - CitadelMediumSoftware EngineerPerform an External Merge Sort with a Heap
Implement an external merge sort simulation that partitions a data stream into memory-bounded sorted runs and merges them using a min-heap.
Coding & AlgorithmsOnsiteExternal SortHeapStreaming - 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 EngineerRefactor a Correct but Quadratic C++ Routine Under a Microsecond Budget
Optimize an inefficient, quadratic tree-resolution routine into a linear-time, cache-friendly implementation suitable for ultra-low-latency execution.
Software Engineering FundamentalsOnline AssessmentTreePerformance OptimizationGraph Traversal - 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 - CitadelMediumSoftware EngineerSimulate 2048 and pack board into uint64
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.
Coding & AlgorithmsOnsite - CitadelHardData ScientistSolve Classic Probability Questions
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.
Statistics & MathOnsiteProbabilityExpectationStochastic Processes - 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 - CitadelHardData ScientistSolve probability and expectation problems
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.
Statistics & MathOnsite - CitadelHardData ScientistSort a nearly sorted array
This question evaluates algorithmic problem-solving skills, specifically understanding sorting under constrained inputs and rigorous time and space complexity analysis.
Coding & AlgorithmsOnsite
Citadel