Reddit interview questions

Showing 1–30 of 36 results

• Analyze CTR Data and Train ModelMedium

  This problem tests the end-to-end workflow of building a CTR prediction model, focusing on feature engineering for high-cardinality categorical data and handling temporal leakage.

  RedditMachine Learning EngineerMachine LearningOnsite
• Build and evaluate click prediction modelsMedium

  This question evaluates skills in supervised probabilistic modeling for click-through rate prediction, including model selection, calibration, evaluation metric choice, cross-validation, hyperparameter tuning, and production concerns like serving and monitoring.

  RedditMachine Learning EngineerMachine LearningTechnical Screen
• Collaborate with PM and Eng as DSEasy

  This question evaluates a data scientist's cross-functional collaboration, prioritization, ownership, stakeholder management, and influencing skills when engaging with product managers and engineers.

  RedditData ScientistBehavioral & LeadershipOnsite
• Communicate and de-risk a non-experimental launchHard

  This question evaluates a data scientist's competency in interpreting causal-inference results from a Synthetic Control, communicating evidence strength and residual risks to executives and skeptical partners, structuring rollout governance and rollback criteria, and managing bias control, dissent and cross-functional accountability.

  RedditData ScientistBehavioral & LeadershipTechnical Screen
• Defend a Schema Decision Through a Real Technical ChallengeMedium

  This question assesses a candidate's ability to articulate the trade-offs behind a core architectural decision, focusing on data modeling, scalability, and technical growth through post-launch reality.

  RedditSoftware EngineerBehavioral & LeadershipTechnical Screen
• Describe a failure and a successMedium

  This question evaluates ownership, communication, accountability, and impact assessment within engineering and machine learning contexts, focusing on incident management, model launches, delivery outcomes, and collaboration.

  RedditMachine Learning EngineerBehavioral & LeadershipOnsite
• Design A/B test for AI chat boxEasy

  This question tests the ability to define metrics, design an A/B testing framework, and account for potential biases when deploying a new AI-powered chat feature.

  RedditData ScientistAnalytics & ExperimentationOnsite
• Design Add, Overwrite, Undo, and Redo for Billing StateHard

  Design an in-memory billing account state manager that supports delta adjustments, absolute balance overwrites, and robust undo/redo capabilities.

  RedditSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• Design Comment Prediction Ranking SystemMedium

  This question assesses the ability to design an end-to-end ML pipeline for ranking comments by predicted user engagement probability, balancing accuracy, latency, and system scalability.

  RedditMachine Learning EngineerML System DesignTechnical Screen
• Design Tennis Scoring with Pluggable RulesMedium

  Design a testable tennis game scoring component with point recording, readable scores, terminal-state handling, and stable player identity. Keep standard Deuce and Advantage rules separate from pluggable alternatives such as no-ad scoring, and discuss audit history and serialization.

  RedditBackend EngineerSoftware Engineering FundamentalsTechnical Screen
• Design a Comment-Likelihood Prediction System with a Focus on Feature and Model ServingMedium

  Design a machine-learning system that predicts how likely a user is to comment on a post, covering label definition, features and model choice, with most of the depth on feature serving and model serving. Tests online and offline feature consistency, feature freshness, latency budgets and safe model deployment.

  RedditMachine Learning EngineerML System DesignOnsite
• Design a Tennis Scoring SystemEasy

  This problem tests your ability to model state transitions, encapsulate logic using object-oriented principles, and implement conditional rule-based scoring in a competitive game.

  RedditMachine Learning EngineerSoftware Engineering FundamentalsTechnical Screen
• Design a feature store with CI/CD and reliabilityHard

  This question evaluates a candidate's competencies in designing scalable, low-latency feature stores and end-to-end ML infrastructure, covering feature ingestion, point-in-time correctness, serving APIs, CI/CD for feature pipelines, metadata/lineage, and reliability engineering.

  RedditSoftware EngineerML System DesignTechnical Screen
• Design a game leaderboard serviceEasy

  This question tests the ability to design a high-throughput, low-latency leaderboard service capable of handling frequent rank updates and read requests for millions of active users.

  RedditSoftware EngineerSystem DesignOnsite
• Design a video recommendation systemMedium

  This question evaluates ML system design competencies for a Machine Learning Engineer, covering infrastructure architecture, logging and observability, feature pipelines, model training/evaluation, serving reliability, and privacy-aware data practices within the ML System Design domain.

  RedditMachine Learning EngineerML System DesignOnsite
• Design comment rankingHard

  This problem evaluates your ability to design a scalable comment ranking system that balances engagement, relevance, and safety, while addressing the challenges of low-latency inference and data freshness.

  RedditMachine Learning EngineerML System DesignOnsite
• Design comment-likelihood prediction platformMedium

  This question evaluates a candidate's competency in ML system design and infrastructure, covering feature pipelines, feature store strategy, training/serving consistency, online inference at high QPS, and production monitoring.

  RedditSoftware EngineerML System DesignOnsite
• Design experiment for ads in chat with budgetsEasy

  This question tests the ability to design an A/B test for a new ad placement in a chat feature while accounting for budget constraints and potential network effects.

  RedditData ScientistAnalytics & ExperimentationOnsite
• Estimate Incremental Search-Ad Revenue Without an A/B TestHard

  Design an evaluation framework to estimate the incremental search-ad revenue of a small-scale manual pilot, incorporating variance reduction, inference under heavy-tailed revenue, and ecosystem cannibalization.

  RedditData ScientistAnalytics & ExperimentationOnsite
• Exclude Cat- or Dog-Related Comments and All Their Replies by Reader ModeMedium

  Given discussion comments that form reply trees, each flagged as being about cats, dogs, both or neither, return every comment a cat person or a dog person should not see, where hiding a comment also hides all of its replies. Tests reasoning over tree structure, edge cases such as missing parents, and complexity analysis.

  RedditMachine Learning EngineerCoding & AlgorithmsOnsite
• Explain How You Use AI in Engineering WorkMedium

  Prepare a concrete account of using AI in engineering, including what you delegated, what information you withheld, and how you verified or rejected its output. Discuss correctness, privacy, licensing, maintainability, and continued human accountability.

  RedditSoftware EngineerBehavioral & LeadershipTechnical Screen
• Explain and Reduce Position Bias in RankingHard

  Assess understanding of position bias in click-based ranking systems, including formalizing the examination hypothesis, estimating observation propensities, training with Inverse Propensity Scoring (IPS), and designing counterfactual evaluation metrics.

  RedditMachine Learning EngineerMachine LearningTechnical Screen
• Find a Word Along One Fixed Direction in a GridMedium

  Search a letter grid for a word along one fixed direction, with explicit diagonal rules, boundaries, and rejection of paths that turn.

  RedditSoftware EngineerCoding & AlgorithmsTechnical Screen
• Find word sequence with 1–2 char changesMedium

  This question evaluates graph traversal and shortest-path search skills, specifically reasoning about BFS vs DFS, string transformation modeling, and algorithmic time/space complexity within the Coding & Algorithms domain.

  RedditSoftware EngineerCoding & AlgorithmsTechnical Screen
• Implement a Stateful Chatter Message StoreMedium

  Design and implement an in-memory message store supporting batch appends, contextual neighborhood queries, text editing with history tracking, and interval merging for read operations.

  RedditSoftware EngineerSoftware Engineering FundamentalsTechnical Screen
• Implement a simplified memcached serverMedium

  This problem tests your ability to design a thread-safe, in-memory key-value store and implement basic command parsing for an asynchronous network service.

  RedditMachine Learning EngineerCoding & AlgorithmsTechnical Screen
• Implement a sliding-window rate limiterMedium

  This problem tests your ability to design a rate-limiting algorithm that calculates traffic volume within a sliding time window to prevent API abuse.

  RedditSoftware EngineerCoding & AlgorithmsOnsite
• Improve Reddit onboardingHard

  This question evaluates product sense, analytical reasoning, experiment design, and cross-functional leadership in the context of improving first-time user onboarding and activation on a community platform, testing competencies in user research, metric definition, prioritization, and validation.

  RedditMachine Learning EngineerBehavioral & LeadershipOnsite
• Justify synthetic control and handle inferenceHard

  This question evaluates understanding of synthetic control methodology, causal identification assumptions, estimation and regularization choices, inference techniques for pointwise and cumulative effects, and diagnostic checks for panel time-series interventions.

  RedditData ScientistStatistics & MathTechnical Screen
• Measure impact of ads-manager automation featureEasy

  This question tests your ability to design an evaluation framework for a new feature, specifically focusing on causal inference, metric selection, and identifying potential biases in a two-sided marketplace.

  RedditData ScientistAnalytics & ExperimentationOnsite