Whatnot interview questions

Showing 1–21 of 21 results

• Build User Journey Path SummaryHard

  This question evaluates the ability to transform unordered user action logs into a trie-like path tree, exercising skills in grouping and time-sorting per user, maintaining stable insertion order, counting distinct users per prefix, and producing deterministic preorder string output.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen
• Build a Tic-Tac-Toe AppMedium

  This question evaluates proficiency in interactive UI development and stateful game logic, including turn management, board state representation, win/draw detection, input validation, and reset flow.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen
• Calculate Monthly Customer RetentionMedium

  A PostgreSQL interview problem about calculating monthly customer retention from activity data. It tests month-level cohort construction, distinct-user counting, correct denominator selection, and handling customers who return across calendar boundaries.

  WhatnotData ScientistData Manipulation (SQL/Python)Technical Screen
• Check Whether a String Can Become a Palindrome by Deleting at Most One CharacterEasy

  A string coding problem that asks whether a lowercase string can be turned into a palindrome by deleting at most one character, returning a boolean. It tests careful handling of mismatched characters, strings that are already palindromes, and an efficient solution for strings of up to 100,000 characters.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen
• Compute a Seven-Day Rolling AverageMedium

  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.

  WhatnotData ScientistData Manipulation (SQL/Python)Technical Screen
• Content Safety FilterMedium

  Tests string tokenization, interval tracking, and Trie-based multi-word pattern matching to redact prohibited phrases from live-stream messages.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen
• Count User Journey PrefixesEasy

  Process timestamped user activity logs to reconstruct chronological action sequences and count the frequency of user journey prefixes up to length k.

  WhatnotSoftware EngineerCoding & AlgorithmsOnline Assessment
• Define Marketplace Success Metrics and Investigate Their MovementMedium

  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.

  WhatnotData ScientistAnalytics & ExperimentationTechnical Screen
• Design a Charity Donation WebsiteMedium

  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.

  WhatnotSoftware EngineerSystem DesignTechnical Screen
• Design a Direct Messaging System for an E-commerce MarketplaceMedium

  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.

  WhatnotSoftware EngineerSystem DesignTechnical Screen
• Design an Online Coding Contest PlatformMedium

  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.

  WhatnotSoftware EngineerSystem DesignTechnical Screen
• Design an Online Coding JudgeEasy

  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.

  WhatnotSoftware EngineerSystem DesignTechnical Screen
• Design trending livestream discoveryMedium

  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.

  WhatnotMachine Learning EngineerML System DesignTechnical Screen
• Dot Product of Two Vectors (Dense, then Sparse)Medium

  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.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen
• Improve and debug the shopping appMedium

  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.

  WhatnotMachine Learning EngineerSystem DesignTechnical Screen
• Knight Dialer: Count Dialable Digit SequencesMedium

  Calculate the number of distinct n-digit phone numbers reachable by standard chess knight moves on a numeric keypad, modulo 10^9 + 7.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen
• Merge Two Sorted ArraysHard

  Implement a linear-time merge of two sorted arrays into a new sorted array using two pointers, preserving duplicates without modifying the input arrays.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen
• Propose and Validate a Mobile App ImprovementMedium

  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.

  WhatnotSoftware EngineerSystem DesignTechnical Screen
• Remove All Adjacent Duplicate PairsHard

  Implement an algorithm to repeatedly eliminate adjacent identical character pairs from a string until no adjacent duplicates remain, handling Unicode inputs in linear time.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen
• Repeatedly Delete Adjacent Duplicate Pairs or Whole Runs of Equal CharactersEasy

  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.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen
• Solve Adjacent-Deletion and Sorted-Square ProblemsEasy

  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.

  WhatnotSoftware EngineerCoding & AlgorithmsTechnical Screen