Reddit Interview Questions
Practice 29 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."
Design Comment Prediction Ranking System
Design an end-to-end machine learning system that powers the following prediction API: ` will_user_comment_on_posts(user_id, post_ids) -> scores ` Inp...
Moderator System with Ranking, Communities, and Demotion
You are designing a system that tracks moderator privileges for an online community using a time-ordered log of moderation actions. Each log record ca...
Design a Tennis Scoring System
Design an object-oriented tennis scoring system for two named players. Part 1: Implement a TennisGame class for a single game. Required API: `python c...
Implement a simplified memcached server
Implement a simplified in-memory key-value store that speaks a small text protocol inspired by memcached. The server stores keys and raw byte values i...
Merge Message Context Windows
You are given a chat history in which each message has a unique integer id and a string content. Message IDs are strictly increasing, and the full his...
Design comment ranking
Design a large-scale ranking system for ordering comments under a post on a community platform similar to Reddit. When a user opens a post, the system...
Model y from x and interpret distributions
Scenario You are given a dataset with one input feature x and a target y. The interviewer asks: “How would you model this?” Later, you are shown a plo...
Analyze CTR Data and Train Model
You are given a notebook-based live coding task for click prediction. A tabular dataset contains the following columns: - post_id: unique identifier f...
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 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...
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...
Design a game leaderboard service
System Design: Game Leaderboard Design a backend service that powers leaderboards for an online game. Core functionality - Players submit score update...
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...
Design A/B test for AI chat box
Context A social platform (e.g., Reddit) plans to launch an AI chat box that answers user questions. The functionality overlaps with the existing Sear...
Justify synthetic control and handle inference
Synthetic Control: Assumptions, Estimation, Inference, and Diagnostics Context You are estimating the causal effect of an intervention on a single tre...
Solve palindrome and list tasks
You are asked to solve two coding problems. 1. Build the shortest palindrome by prepending characters: Given a string s, add characters only to the fr...
Build and evaluate click prediction models
Click-Through Rate (CTR) Prediction: Build, Compare, and Justify Models Context You are given a tabular dataset for binary click prediction (click = 1...
Collaborate with PM and Eng as DS
Question As a Data Scientist working with Product Managers and Engineers: 1. How do you structure collaboration (requirements, timelines, ownership)? ...
Measure impact of ads-manager automation feature
Context An Ads Manager product has new automation features (e.g., auto-bidding, auto-budgeting, auto-creative suggestions). You need to measure the fe...