practice a little every day, paws crossed ♡
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
- Questions
- 546
- Companies
- 11
- Topics
- 8
- Languages
Showing 541–570 of 2336 results
- 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 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 - 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 - 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 - 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 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 - 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 - 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 - 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 - 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 - Citadel SecuritiesMediumSoftware EngineerDetect Currency Arbitrage and Return a Profitable Conversion Cycle
Given a list of currency conversion rates, determine whether an arbitrage opportunity exists and return a sequence of conversions that ends in the starting currency with more money than it began with. Tests graph modeling, cycle detection, reconstruction of the profitable sequence, and handling of floating-point precision.
Software Engineering FundamentalsOnsite - Citadel SecuritiesMediumSoftware EngineerThread-Safe Producer-Consumer Queue: Mutex, Then Spin Lock, Then Lock-Free
Implement a thread-safe producer-consumer queue in C++, first with a mutex, then with a spin lock, then as a lock-free design with explicit memory ordering. Tests the C++ memory model, contention and cache effects, blocking versus spinning, and where memory is allocated on the hot path.
Software Engineering FundamentalsOnsite - CitiMediumSoftware EngineerExplain OS and networking basics
This question evaluates a candidate's understanding of operating system and networking fundamentals, covering processes, threads and context switching, concurrency versus parallelism, TCP/UDP and flow versus congestion control, and the end-to-end web request and browser rendering pipeline.
System DesignOnsite - CitiMediumSoftware EngineerExplain data structure fundamentals
This question evaluates understanding of data structure fundamentals, specifically hash map internals (hashing, collision resolution strategies, load factor, and resizing), time complexity analysis for search/insert/delete, contrasts between arrays and linked lists for random access and insertion, and typical use cases and complexities for stacks versus queues. It is commonly asked in technical interviews to assess algorithmic thinking and the ability to reason about performance trade-offs and appropriate data structure selection; domain: Coding & Algorithms; level: tests both conceptual understanding and practical application.
Coding & AlgorithmsOnsite - CitiMediumSoftware EngineerSolve two logic brain teasers
This pair of puzzles evaluates logical deduction and optimization competencies—one testing information-theoretic reasoning with constrained ternary comparisons and the other testing sequencing and scheduling trade-offs for minimal total time—and belongs to the Cognitive Ability / Logic category.
Statistics & MathOnsite - CitiMediumSoftware EngineerWalk through resume and impact
This question evaluates a candidate's ability to communicate a coherent career narrative and demonstrate technical ownership, decision-making, trade-off analysis, and metrics-driven impact within a software engineering context, testing competencies in leadership, product sense, and measurable delivery under the Behavioral & Leadership category.
Behavioral & LeadershipOnsite - ClickupMediumSoftware EngineerDesign weekly comment digest
This question evaluates understanding of scalable system architecture, integration with external ML services, handling rate limits, reliable scheduling and delivery, data modeling for aggregation and deduplication, and fault-tolerant ranking under load.
System DesignOnsite - ClickupMediumSoftware EngineerProcess document edit events
This question evaluates implementing and manipulating a line-based document through sequential event processing, emphasizing array/list operations, string handling, and state management; it belongs to the Coding & Algorithms domain and tests data-structure and input-event processing competency.
Coding & AlgorithmsOnsite - CloudKitchensMediumSoftware EngineerDesign real-time kitchen order fulfillment system
This question evaluates a candidate's competency in designing real-time backend systems, emphasizing concurrency control, stateful resource allocation, time-sensitive freshness constraints, efficient eviction policies, and action logging.
System DesignOnsite - CloudflareMediumSoftware EngineerDesign an encrypted log collection system
This question tests the ability to design a distributed, high-throughput ingestion pipeline that ensures log confidentiality and integrity using encryption at rest and in transit.
System DesignOnsiteSecurityDistributed SystemsEncryption - CloudflareMediumSoftware EngineerImplement a rule-based rate limiter
Design and implement a multi-rule rate limiter that tracks client request quotas across matching path prefixes using a sliding time window.
Coding & AlgorithmsOnsitesliding-windowdata-structuresdesign - Cockroach LabsMediumSoftware EngineerPoint-in-Time Reads from a Timestamped Key-Value Store
Build a versioned key-value store whose reads return the value a key held at a given timestamp: the latest write at or before that time, or an empty string if there is none. Tests choosing a per-key data layout that keeps point-in-time lookups fast across up to 200,000 operations.
Coding & AlgorithmsOnsite - Cockroach LabsMediumSoftware EngineerPresent and Defend an End-to-End Project You Owned: Architecture, Choices, Challenges
A choose-your-own system design round: present a core project you owned end to end at a previous job, then defend its architecture, technology choices and hardest challenges under detailed probing. Tests depth of ownership, trade-off reasoning and the ability to move from a diagram to concrete mechanisms.
System DesignOnsite - CohereMediumSoftware EngineerDelete One '5' From a Digit String to Get the Largest Number
Given a digit string containing at least one 5, delete exactly one 5 so the remaining string has the largest possible numeric value, keeping any leading zeros. This intern online-assessment problem tests reasoning about how each digit position affects a number and careful handling of repeated digits.
Coding & AlgorithmsOnsite - CoinbaseMediumSoftware EngineerAnalyze food-delivery data
This interview question evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer for Analyze food-delivery data states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.
Coding & AlgorithmsOnsite - CoinbaseMediumSoftware EngineerCompute Total Manual Distance
This problem tests your ability to simulate a state-based movement process and calculate cumulative distance based on a non-monotonic set of instructions.
Coding & AlgorithmsOnsiteArraysSimulationMath - CoinbaseMediumSoftware EngineerCompute delivery metrics and top-K queries
Compute delivery metrics and top-K queries evaluates SQL or pandas logic, joins, grouping, window functions, null handling, edge cases, and validation in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.
Data Manipulation (SQL/Python)Onsite
Citadel
Citadel Securities
Citi
Cloudflare
Cohere
Coinbase