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Software Engineer 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
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- 546
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- 11
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Showing 1441–1470 of 5874 results
- CitadelMediumSoftware EngineerCompute Every Fixed-Size Submatrix Sum
Compute every contiguous fixed-size submatrix sum without mutating the input, using a padded two-dimensional prefix grid to answer each window in constant time.
Coding & AlgorithmsOnsite - CitadelHardSoftware EngineerCompute Statistics from a Frequency Array
Compute count, minimum, maximum, mean, median, mode, and population standard deviation directly from a 256-bin frequency array. Use weighted moments and cumulative ranks without expanding samples, define empty-data behavior and ties, and address overflow and numerical precision.
Statistics & MathTechnical Screen - CitadelMediumSoftware EngineerCompute max team size with a core interval
This question evaluates algorithmic problem-solving around interval overlap and time-complexity optimization, measuring the ability to determine the maximum team size given a core interval while reasoning about interval intersections and scalability; it is commonly asked to assess correctness and subquadratic runtime thinking, categorized under Coding & Algorithms and emphasizing practical algorithmic implementation. The follow-up evaluates combinatorics and counting under adjacency constraints with modular arithmetic and efficient handling of large parameters, commonly posed to test recurrence reasoning and scalable counting approaches, falling under combinatorics/dynamic programming and emphasizing conceptual understanding linked to practical algorithmic efficiency.
Coding & AlgorithmsOnline Assessment - CitadelMediumSoftware EngineerCompute maximum later-earlier difference
This problem tests your ability to optimize an O(n^2) brute-force search into an O(n) linear-time solution using a single-pass scan while maintaining state variables.
Coding & AlgorithmsOnline AssessmentArraysOptimizationGreedy - CitadelMediumSoftware EngineerDescribe a Difficult Challenge and How You Resolved It
Practice answering a difficult-project behavioral question with one specific, decision-rich story that separates personal actions from team contributions. The sample response shows how to diagnose retry amplification in a latency incident, negotiate a safe degradation, measure the canary result, acknowledge residual risk, and explain what changed afterward.
Behavioral & LeadershipOnsite - CitadelMediumSoftware EngineerDescribe current work and relocation willingness
This question evaluates leadership, ownership, communication, technical depth in system design and project execution, and logistical flexibility regarding relocation by asking for current responsibilities, a detailed project deep-dive, and relocation constraints.
Behavioral & LeadershipHR Screen - CitadelMediumSoftware EngineerDesign Inventory Availability and Order Placement
Design e-commerce inventory availability and order reservation without overselling under concurrent requests. Define on-hand, reserved, and available invariants; atomic multi-item placement; idempotent retries; expiration; and optimistic versus pessimistic control for hot SKUs.
System DesignTechnical Screen - CitadelMediumSoftware EngineerDesign a Course Registration System
Design a course registration system with relational models and APIs for enrollment, dropping, schedules, waitlists, and course browsing. The solution explains transactional capacity protection, idempotent retries, re-enrollment without duplicate rows, FIFO promotion, outbox notifications, and tests for final-seat races.
System DesignOnsite - CitadelMediumSoftware EngineerDesign a Low-Latency Metrics and Alerting Platform
Design a high-throughput, multi-tenant metrics ingestion and alerting engine capable of triggering critical alerts within two seconds. The question evaluates your knowledge of streaming architectures, time-series storage, cardinality management, and fault-tolerant notification delivery.
System DesignOnsiteTime SeriesDistributed SystemsStreaming - CitadelMediumSoftware EngineerDesign a Thread-Safe Shared Counter
This question evaluates concurrency and synchronization competencies, including atomicity, race conditions, concurrent data structures, and cross-process coordination for maintaining exact per-key counts.
Software Engineering FundamentalsTechnical Screen - CitadelHardSoftware EngineerDesign a low-latency trading platform
This question tests the ability to architect a high-throughput, sub-millisecond trading system while balancing strict deterministic latency requirements with necessary safety checks.
System DesignOnsiteHFTLow-LatencyConcurrency - CitadelHardSoftware EngineerDesign a low-latency trading system
This question evaluates expertise in designing low-latency, high-determinism electronic trading systems, covering order matching, market data ingestion and publish, partitioning/sharding, persistence for auditability, idempotency, pre-trade risk controls, and operational reliability.
System DesignTechnical Screen - CitadelMediumSoftware EngineerDesign a token manager with lazy expiration
This problem tests your ability to design a token management system that supports efficient retrieval, updates, and lazy removal of expired tokens using a combination of a hash map and a priority queue.
Coding & AlgorithmsTechnical ScreenHash MapHeapTTL - CitadelMediumSoftware EngineerDesign alerting for application-to-exchange mappings
This question evaluates understanding of real-time stream processing, alerting policy design, and distributed state coordination for application-to-exchange mappings, testing competencies in scalability, correctness under partitioning and duplication, and efficient aggregation of high-volume event streams.
System DesignOnsite - CitadelMediumSoftware EngineerDesign an Authenticated Online Shopping Service
Design an authenticated online shopping service with secure signup and login, user-owned carts, product browsing, and retry-safe order creation. The solution covers password hashing, session rotation, CSRF defenses, resource-level authorization, idempotency keys, immutable order snapshots, recovery tokens, and horizontal-access tests.
System DesignOnsite - CitadelMediumSoftware EngineerDesign dynamic weighted random sampling with updates
This question evaluates a candidate's ability to design and analyze dynamic data structures that support weighted random sampling with inserts and deletes, testing skills in algorithm design, complexity analysis, and randomized sampling under large numeric constraints.
Coding & AlgorithmsOnsite - CitadelHardSoftware EngineerDiscuss a Project You Are Proud Of and How You Work
Use one truthful project to explain what you are proud of, what changed in your thinking, and how you organize a normal workday. Connect personal decisions and measurable impact to later behavior while showing realistic prioritization, collaboration, focused work, and adaptability.
Behavioral & LeadershipTechnical Screen - CitadelHardSoftware EngineerDiscuss queues, NoSQL, and concurrency
This question evaluates understanding of distributed messaging systems, delivery semantics, push versus pull consumption models, NoSQL versus relational storage trade-offs, and concurrency control including deadlock concepts.
System DesignTechnical Screen - CitadelHardSoftware EngineerEvery MEX Reachable With At Most One Bounded Increment
A coding problem about memory blocks with values below n: using at most one increment of a single value, never raising a value to n, list every minimum excluded value (MEX) the array can end up with. It tests careful case analysis of how one increment can open or fill a gap, handling duplicate values, and returning the sorted answer efficiently.
Coding & AlgorithmsOnline Assessment - CitadelHardSoftware EngineerEvery Reachable Priority Gap After At Most One Bounded Bump
Given n network ports each tagged with a priority code below n, find every value the lowest unused priority code could take after at most one bounded increment. Tests careful case analysis of how a single bump opens or closes a gap, and returning the answer efficiently.
Coding & AlgorithmsOnline Assessmentarrayscountingmex - CitadelMediumSoftware EngineerExplain JS types, Promises, Maps, WebSockets
Explain JS types, Promises, Maps, WebSockets evaluates requirements, assumptions, structured reasoning, trade-offs, and verification in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.
Software Engineering FundamentalsTechnical Screen - CitadelMediumSoftware EngineerExplain career motivations and choices
This question evaluates self-awareness, career motivation, role-fit, decision-making, and communication skills for a Software Engineer by probing career values, educational and internship choices, and motivation for entering the finance industry.
Behavioral & LeadershipTechnical Screen - CitadelMediumSoftware EngineerFind earliest common meeting slot
This question evaluates proficiency with interval manipulation, timeline merging, and algorithmic reasoning for scheduling constraints, measuring competency in handling sorted interval lists, edge-case sanitization, and complexity analysis.
Coding & AlgorithmsTechnical Screen - CitadelMediumSoftware EngineerFind the Index Range of a Target in a Sorted Array
Implement an algorithm to find the first and last index of a target value in a sorted array in O(log n) time.
Coding & AlgorithmsTechnical Screenbinary-searcharrayscitadel - CitadelMediumSoftware EngineerFind the Shortest Target-Sum Path
This problem tests your ability to navigate binary trees using recursion or iterative traversal while maintaining state to find a path that meets a specific sum criteria with the smallest number of nodes.
Coding & AlgorithmsTechnical ScreenTreesDFSRecursion - CitadelHardSoftware EngineerFirst Free Locker Number After One Tag Bump
Given locker tags in [0, n-1], list every possible smallest missing tag after at most one capped +1 adjustment. Tests MEX reasoning, careful case analysis around duplicates, and an O(n) solution.
Coding & AlgorithmsOnline Assessmentarrayscountingcase-analysis - CitadelMediumSoftware EngineerGenerate Prefix-Based Product Suggestions
Generate up to three lexicographically smallest product suggestions for every prefix of a search word, with efficient handling once a prefix has no matches.
Coding & AlgorithmsOnsite - CitadelMediumSoftware EngineerHarbor Clash: A Two-Captain Terminal Naval Game, Setup Then Combat
Write a runnable two-player hidden-fleet game for the terminal: captains place vessels via typed commands with full validation, then alternate firing until one fleet is sunk; tests modeling, parsing, turn flow and shipping working code fast.
Software Engineering FundamentalsTechnical Screenobject-oriented-designgameinput-validation - CitadelMediumSoftware EngineerHow do you handle conflict at work?
This question evaluates interpersonal skills such as conflict resolution, communication, accountability, and leadership by asking about a concrete disagreement with a teammate in a software engineering context.
Behavioral & LeadershipOnsite - 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
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