Reddit Interview Questions
Practice 35 real Reddit interview questions for 2026. Covers all top categories — coding & algorithms, ML and system design, analytics & experimentation, and behavioral leadership — across Software Engineer, Machine Learning Engineer, and Data Scientist roles. Real interview questions from actual interviews with detailed solutions; use this guide for interview preparation so you can target the exact skills Reddit evaluates. Expect a coding-and-systems-heavy loop: Software Engineer questions concentrate on merging message context windows, scalable game leaderboards, sliding-window rate limiters, feature-store CI/CD and reliability, comment-likelihood prediction platforms, and small competitive string/sequence puzzles. Machine Learning Engineer problems mix onboarding and recommendation-system design (comment ranking, video recs), click-prediction modeling, data-loading/JSON edge cases, and short algorithmic tasks. Data Scientist prompts emphasize A/B and non-experimental causal evaluation for ads and chat features (including synthetic-control reasoning), experiment design and power, SQL on US-based users and active forums, probability/estimation puzzles, prioritization, and communicating risk to PMs and engineers. Prep by drilling timed coding, system-design tradeoffs, experiment design and causal frameworks, SQL windowing and performance, production-model evaluation, and clear STAR stories for leadership questions.
"I got asked a hardcore MCM DP question and I saw it on PracHub as well. Solved that question in 5 minutes. Without PracHub I doubt I could solve it in 5 hours. Though somehow didn't get hired, perhaps I guess I solved it too fast? /s"
"Believe me i'm a student here jn US. Recently interviewed for MSFT. They asked me exact question from PracHub. I saw it the night before and ignored it cause why waste time on random sites. I legit wanna go back and redo this whole thing if I had chance. Not saying will work for everyone but there is certainly some merit to that website. And i'm gonna use it in future prep from now on like lc tagged"
"10 years of experience but never worked at a top company. PracHub's senior-level questions helped me break into FAANG at 35. Age is just a number."
"I was skeptical about the 'real questions' claim, so I put it to the test. I searched for the exact question I got grilled on at my last Meta onsite... and it was right there. Word for word."
"Got a Google recruiter call on Monday, interview on Friday. Crammed PracHub for 4 days. Passed every round. This platform is a miracle worker."
"I've used LC, Glassdoor, and random Discords. Nothing comes close to the accuracy here. The questions are actually current — that's what got me. Felt like I had a cheat sheet during the interview."
"The solution quality is insane. It covers approach, edge cases, time complexity, follow-ups. Nothing else comes close."
"Legit the only resource you need. TC went from 180k -> 350k. Just memorize the top 50 for your target company and you're golden."
"PracHub Premium for one month cost me the price of two coffees a week. It landed me a $280K+ starting offer."
"Literally just signed a $600k offer. I only had 2 weeks to prep, so I focused entirely on the company-tagged lists here. If you're targeting L5+, don't overthink it."
"Coaches and bootcamp prep courses cost around $200-300 but PracHub Premium is actually less than a Netflix subscription. And it landed me a $178K offer."
"I honestly don't know how you guys gather so many real interview questions. It's almost scary. I walked into my Amazon loop and recognized 3 out of 4 problems from your database."
"Discovered PracHub 10 days before my interview. By day 5, I stopped being nervous. By interview day, I was actually excited to show what I knew."
"I recently cleared Uber interviews (strong hire in the design round) and all the questions were present in prachub."
"The search is what sold me. I typed in a really niche DP problem I got asked last year and it actually came up, full breakdown and everything. These guys are clearly updating it constantly."
Implement a Stateful Chatter Message Store
Implement a Stateful Chatter Message Store Design a Chatter class that can load multiple ordered batches of messages, save its current messages, retur...
Defend a Schema Decision Through a Real Technical Challenge
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Estimate Incremental Search-Ad Revenue Without an A/B Test
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Design Comment Prediction Ranking System
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Debug and Improve a Load Balancer
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Design Tennis Scoring with Pluggable Rules
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Design a Tennis Scoring System
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Moderator System with Ranking, Communities, and Demotion
This question tests practical data structure design and object-oriented system modeling, requiring the implementation of a hierarchical moderator mana...
Merge Message Context Windows
This question evaluates a candidate's skill in designing efficient algorithms and appropriate data-structure use for merging overlapping message conte...
Design comment ranking
This question evaluates competency in designing large-scale machine learning ranking systems, testing skills such as candidate generation, label and t...
Model y from x and interpret distributions
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Design a video recommendation system
Scenario You are designing an ML-driven video recommendation product (home feed + “up next”) for a consumer app. The interviewer focuses heavily on in...
Analyze CTR Data and Train Model
This question evaluates end-to-end supervised machine learning competencies for tabular click-through rate prediction, including exploratory data anal...
Explain How You Use AI in Engineering Work
Explain How You Use AI in Engineering Work Prompt How do you use AI-assisted tools in your day-to-day engineering work? Give one concrete example, exp...
Design A/B test for AI chat box
This question evaluates skills in experimental design, product analytics, metrics selection, and causal inference relevant to a Data Scientist role in...
Query US-based users and most active forums
You are given user and post data for an online forum platform. Tables (schemas) Assume the following tables: users - user_id BIGINT (PK) - home_countr...
Improve Reddit onboarding
How would you improve the onboarding experience for new users on a community platform similar to Reddit? Assume the goal is to help first-time users q...
Describe a failure and a success
Questions 1. Tell me about a time you failed (or something didn’t go as planned). What happened, what did you learn, and what would you do differently...
Design comment-likelihood prediction platform
Scenario You’re building an ML platform component that serves a model to predict the likelihood that a user will comment on a given post. The intervie...
Design a causal evaluation without A/B testing
Non-Randomized Launch Decision via Synthetic Control: Complete Analysis Plan You need to make a go/no-go decision for a high-impact feature that canno...