practice a little every day, paws crossed ♡
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 9211–9240 of 9403 results
- WhatnotMediumData ScientistCompute a Seven-Day Rolling Average
A PostgreSQL interview problem about computing a seven-day rolling average from dated observations. Candidates must use window frames carefully, preserve the requested grain, handle incomplete history, and return deterministically ordered results.
Data Manipulation (SQL/Python)Technical Screen - WhatnotMediumSoftware EngineerContent Safety Filter
Tests string tokenization, interval tracking, and Trie-based multi-word pattern matching to redact prohibited phrases from live-stream messages.
Coding & AlgorithmsTechnical ScreenStringTrieHash Table - WhatnotEasySoftware EngineerCount User Journey Prefixes
Process timestamped user activity logs to reconstruct chronological action sequences and count the frequency of user journey prefixes up to length k.
Coding & AlgorithmsOnline Assessmenthash-mapsortingstrings - WhatnotMediumData ScientistDefine Marketplace Success Metrics and Investigate Their Movement
A product analytics interview about defining success for a two-sided marketplace and diagnosing an unexpected metric movement. It tests metric decomposition, cohort and funnel analysis, instrumentation checks, and the ability to separate product effects from mix shifts.
Analytics & ExperimentationTechnical Screen - WhatnotMediumSoftware EngineerDesign a Charity Donation Website
Tests your ability to architect a resilient, high-throughput charity donation platform with strict payment idempotency, asynchronous transaction processing, real-time campaign counters, and financial auditability.
System DesignTechnical ScreenPaymentsDistributed SystemsIdempotency - WhatnotMediumSoftware EngineerDesign a Direct Messaging System for an E-commerce Marketplace
Design a scalable 1:1 direct messaging platform for an e-commerce marketplace that supports real-time chat, message ordering, read receipts, and offline push notifications across multiple devices.
System DesignTechnical ScreenDistributed SystemsMessagingWebSockets - WhatnotMediumSoftware EngineerDesign an Online Coding Contest Platform
This problem tests your ability to design a distributed architecture for an online coding platform, focusing on secure code execution, high-concurrency submission handling, and real-time leaderboard updates.
System DesignTechnical ScreenDistributed SystemsSandboxingScalability - WhatnotEasySoftware EngineerDesign an Online Coding Judge
This question evaluates system design and scalability skills, including distributed architectures, API and data model design, secure sandboxed code execution, artifact storage with signed URLs, and operational concerns such as observability, fault tolerance, and security.
System DesignTechnical Screen - WhatnotMediumMachine Learning EngineerDesign trending livestream discovery
This question evaluates expertise in designing end-to-end ML-driven recommendation systems, including competencies in real-time feature engineering, candidate generation, model serving, business-rule integration, monitoring, experimentation, and operational trade-offs for live content.
ML System DesignTechnical Screen - WhatnotMediumSoftware EngineerDot Product of Two Vectors (Dense, then Sparse)
Tests data structure design and algorithmic optimization for sparse vector operations, transitioning from standard array traversal to pointer-based or hash-based solutions that scale with non-zero elements.
Coding & AlgorithmsTechnical Screenarrayhash-tabletwo-pointers - WhatnotMediumMachine Learning EngineerImprove and debug the shopping app
This question evaluates product-minded engineering competencies including product intuition, user-experience assessment, telemetry-driven diagnostics, funnel and segmentation analysis, and debugging/observability skills relevant to a machine learning engineer.
System DesignTechnical Screen - WhatnotMediumSoftware EngineerKnight Dialer: Count Dialable Digit Sequences
Calculate the number of distinct n-digit phone numbers reachable by standard chess knight moves on a numeric keypad, modulo 10^9 + 7.
Coding & AlgorithmsTechnical Screendynamic-programminggraphcombinatorics - WhatnotHardSoftware EngineerMerge Two Sorted Arrays
Implement a linear-time merge of two sorted arrays into a new sorted array using two pointers, preserving duplicates without modifying the input arrays.
Coding & AlgorithmsTechnical Screenarraystwo-pointerssorting - WhatnotMediumSoftware EngineerPropose and Validate a Mobile App Improvement
This question evaluates product design and system-design skills for mobile applications, including product thinking, high-level implementation planning, experimentation design, and metrics-driven decision-making within the system design category.
System DesignTechnical Screen - WhatnotHardSoftware EngineerRemove All Adjacent Duplicate Pairs
Implement an algorithm to repeatedly eliminate adjacent identical character pairs from a string until no adjacent duplicates remain, handling Unicode inputs in linear time.
Coding & AlgorithmsTechnical Screenstackstringsunicode - WhatnotEasySoftware EngineerRepeatedly Delete Adjacent Duplicate Pairs or Whole Runs of Equal Characters
A string coding problem with two modes: repeatedly delete pairs of equal adjacent characters, or, as the follow-up, delete whole runs of equal adjacent characters, always the leftmost run first, and return what remains. It tests simulating cascading deletions efficiently and handling runs that merge after a deletion.
Coding & AlgorithmsTechnical Screen - WhatnotEasySoftware EngineerSolve Adjacent-Deletion and Sorted-Square Problems
This question evaluates skills in string manipulation and pattern-removal algorithms for adjacent duplicates and k-sized group deletions, as well as array processing and merging techniques for producing sorted squares; it tests understanding of relevant data-structure concepts and merging/two-pointer strategies within the Coding & Algorithms domain. It is commonly asked to assess algorithmic efficiency, correctness under large input constraints and tricky edge cases (such as cascading deletions and negative values), and is primarily a practical implementation task that emphasizes complexity analysis over purely theoretical reasoning.
Coding & AlgorithmsTechnical Screen - WhoopHardiOS EngineerDesign a BLE Command Handler
This question evaluates a candidate's understanding of BLE communication, concurrency control, command queuing and sequencing, timeout and failure policies, lifecycle and cancellation handling, and testability for production-grade mobile applications.
System DesignTechnical Screen - Wikimedia FoundationMediumProduct ManagerDesign a strategy to grow reader donations to Wikipedia while keeping it ad-free
A product strategy interview question asking how a Wikimedia Foundation product manager would increase donations to Wikipedia while keeping it free and ad-free. It tests choosing a goal and metric, segmenting readers and donors, diagnosing where the donation funnel leaks, prioritizing ideas, and protecting reader trust.
Product Design & StrategyOther - WorkdayMediumSoftware EngineerBuild a Fuzzy Keyword Index
This problem tests your ability to design an efficient data structure for performing fuzzy keyword lookups using edit distance constraints on a static corpus of strings.
Coding & AlgorithmsOnsiteStringsTrieHash Map - WorkdayMediumSoftware EngineerDesign AI-Powered Document Search
This question assesses the ability to design an end-to-end, scalable pipeline for ingesting, processing, and indexing heterogeneous documents (PDFs, images, text files) to support AI-driven semantic search.
ML System DesignOnsiteSystem DesignML EngineeringPipelines - WorkdayEasySoftware EngineerExplain What You Value in Your Next Engineering Role
This question assesses your self-awareness, alignment with organizational culture, and your ability to articulate professional priorities through past experiences.
Behavioral & LeadershipHR ScreenCareer GrowthCompany CultureSelf-Reflection - WorldquantHardSoftware EngineerCompare Functional and Object-Oriented Python Design
Design and contrast functional versus object-oriented architectures for an in-memory record transformation and enrichment pipeline in Python that requires runtime configuration and cached lookup state. Evaluate both paradigms across state isolation, testability, edge cases, and thread safety.
Software Engineering FundamentalsTechnical Screenpythonsystem-design-principlesfunctional-programming - WorldquantMediumSoftware EngineerCount Unordered Combinations of Unlimited Coins
Count distinct ways to reach a target with unlimited coins, treating different orders of the same denominations as one combination.
Coding & AlgorithmsOnline Assessment - WorldquantMediumData ScientistFind the Expected Number of Record Maxima
A permutation of the distinct values `1` through `100` is revealed from left to right. Explain the assumptions and derivation clearly, check edge cases, and show how the result changes when those assumptions no longer hold.
Statistics & MathTechnical Screen - WorldquantMediumData ScientistPrice a Sequential Four-Box Search Game
Four boxes contain one \$100 prize. Explain the assumptions and derivation clearly, check edge cases, and show how the result changes when those assumptions no longer hold.
Statistics & MathTechnical Screen - XPengMediumData EngineerBuild a Least-Recently-Used Store
This question evaluates understanding of caching and eviction policies and practical proficiency with data structures such as hash tables and ordered collections for tracking and updating recency.
Coding & AlgorithmsTechnical Screen - XPengHardMachine Learning EngineerDesign and train a PPO pipeline
This question evaluates proficiency in designing and training Proximal Policy Optimization (PPO) pipelines, covering environment interfacing, observation/action design, reward shaping, rollout and advantage estimation, hyperparameterization, normalization, parallelization, evaluation, and sim‑to‑real considerations.
ML System DesignTechnical Screen - XPengMediumMachine Learning EngineerDiscuss resume and company fit
This question evaluates a candidate's competence in reinforcement learning and production-grade ML systems, focusing on technical decision-making, measurable project impact, communication of role and motivation, and leadership in planning within the Behavioral & Leadership domain.
Behavioral & LeadershipTechnical Screen - XPengHardMachine Learning EngineerExplain PPO and Transformer basics
This question evaluates mastery of reinforcement learning algorithms (PPO, policy gradients, TRPO), value-function theory and actor–critic methods (Bellman equations), on- versus off-policy trade-offs and training-stability techniques (clipping, entropy, advantage estimation), plus sequence-modeling fundamentals with Transformers (self-attention, positional encodings and complexity comparisons). It is commonly asked to judge reasoning about algorithmic trade-offs, sample efficiency and stability in practical ML systems, and falls under the Machine Learning domain—specifically reinforcement learning and deep learning/sequence modeling—testing both conceptual understanding and practical application.
Machine LearningTechnical Screen
Whatnot
Worldquant
XPeng