OpenAI
Leading AI research laboratory developing state-of-the-art foundation models like GPT-4.
5 Rounds
~21 Days
Very Hard
The Interview Loop
Recruiter Screen (30 min)
Standard fit check, behavioral questions, and resume overview.
Technical Loop (3-4 Rounds)
Deep dive into domain knowledge, coding, and system design.
Interview Question Bank
Backend Engineer
•
Coding
•
hard
Given a stream of nested JSON chunks (which may be fragmented), write a parser that yields valid JSON objects as soon as they are fully formed.
#String Manipulation
#Parsing
#Stacks
Backend Engineer
•
Coding
•
medium
Implement a thread-safe LRU Cache with a Time-To-Live (TTL) for each entry. This would be used to cache recent prompt embeddings.
#Hash Maps
#Linked Lists
#Concurrency
Backend Engineer
•
Coding
•
medium
Write a function to merge K sorted streams of tokens into a single sorted stream. Assume the streams are coming from different backend model replicas.
#Heaps
#Streaming Data
#Pointers
Backend Engineer
•
Coding
•
medium
Implement a token bucket rate limiter that can handle both requests-per-minute and tokens-per-minute limits simultaneously.
#Concurrency
#Data Structures
#Rate Limiting
Backend Engineer
•
Coding
•
easy
Given an array of API request start and end times, calculate the maximum number of concurrent requests the server handled.
#Arrays
#Sorting
#Sweep Line
Backend Engineer
•
Coding
•
medium
Write a program to resolve dependencies for a set of AI agents. Given a list of agents and their dependencies, output a valid execution order.
#Graphs
#Topological Sort
#BFS/DFS
Backend Engineer
•
Coding
•
hard
Implement a distributed task queue executor. You have a central queue and multiple worker nodes. Ensure tasks are executed exactly once.
#Distributed Systems
#Concurrency
#State Machines
Backend Engineer
•
Coding
•
medium
Find the longest substring with at most K distinct characters. (Used to optimize context window parsing).
#Sliding Window
#Hash Maps
#Strings
Backend Engineer
•
Coding
•
hard
Implement a text justification algorithm. Given an array of words and a maximum width, format the text such that each line has exactly the maximum width.
#String Manipulation
#Greedy Algorithms
Backend Engineer
•
Coding
•
hard
Serialize and deserialize an N-ary tree. This is used to represent branched conversation threads where users edit previous prompts.
#Trees
#Serialization
#DFS/BFS
Backend Engineer
•
Coding
•
medium
Implement a Trie data structure optimized for fast prefix matching to detect blocked keywords in a streaming prompt.
#Trees
#Trie
#String Matching
Cloud Engineer
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Coding
•
medium
Implement a task scheduler that takes a list of tasks with dependencies and executes them in the correct order. If a cycle is detected, throw an error.
#Graphs
#Topological Sort
#DFS/BFS
Cloud Engineer
•
Coding
•
hard
Write a function to find the shortest path in a network of microservices to identify the root cause of a cascading failure, given a graph of service dependencies and their current error rates.
#Graphs
#Dijkstra
#BFS
Cloud Engineer
•
Coding
•
medium
Given a list of IP CIDR blocks, write a function to merge all overlapping blocks and return the minimized list of CIDRs.
#Intervals
#Networking
#Python/Go
Cloud Engineer
•
Coding
•
medium
Write a Python script to parse a massive stream of distributed logs, identify spikes in specific HTTP 5xx errors, and output the top 3 offending IP addresses.
#Python
#Log Parsing
#Data Structures
#Streaming
Cloud Engineer
•
Coding
•
hard
Implement a token bucket rate limiter in Python or Go. Explain how you would adapt this to work across a distributed cluster of API gateways.
#Rate Limiting
#Distributed Systems
#Redis
Cloud Engineer
•
Coding
•
easy
Implement a basic load balancer algorithm in code that routes requests to a pool of backend servers using Weighted Round Robin.
#Load Balancing
#Data Structures
#Math
Data Engineer
•
Coding
•
hard
Implement a MinHash and Locality-Sensitive Hashing (LSH) algorithm to find near-duplicate documents in a massive corpus of web text.
#Hashing
#Probability
#Text Processing
#Big Data
Data Engineer
•
Coding
•
medium
Implement a function to merge overlapping text intervals (e.g., highlighting spans in a document).
#Sorting
#Arrays
#Intervals
Data Engineer
•
Coding
•
medium
Given a stream of API requests, implement a sliding window rate limiter.
#Data Structures
#Concurrency
#Queues
Data Engineer
•
Coding
•
medium
Write a Python generator to efficiently parse a 500GB JSONL file containing conversation logs without loading the whole file into memory.
#Python
#Memory Management
#Generators
#File I/O
Data Engineer
•
Coding
•
easy
Write a function to merge overlapping time intervals. We use this to calculate the total active compute time for GPU clusters given a log of job start and end times.
#Intervals
#Sorting
#Python
Data Engineer
•
Coding
•
hard
Find the top K most frequent tokens in a continuous, infinite stream of text data.
#Streaming Algorithms
#Heaps
#Count-Min Sketch
Data Engineer
•
Coding
•
medium
Implement a sliding window rate limiter for the OpenAI API that can handle high concurrency.
#Data Structures
#Concurrency
#Queues
Data Engineer
•
Coding
•
medium
Write a Python function to parse a massive JSONL file containing web crawl data, filter out documents with a high proportion of non-alphanumeric characters (spam/code), and yield batches of clean text. Assume the file is significantly larger than available RAM.
#Python
#Generators
#Memory Management
#Text Processing
Data Engineer
•
Coding
•
hard
Implement a rate limiter for our API. Given a stream of requests, allow a maximum of N requests per minute per user. If a user exceeds this, drop the requests. Optimize for high concurrency and minimal latency.
#Rate Limiting
#Concurrency
#Data Structures
#Redis
Data Engineer
•
Coding
•
medium
Given a list of text spans representing PII (Personally Identifiable Information) redactions with start and end indices, write a function to merge overlapping intervals efficiently.
#Arrays
#Sorting
#Intervals
Data Engineer
•
Coding
•
medium
Given a list of conversational turns (user prompt, assistant response) with timestamps and session IDs, write a function to reconstruct the conversation threads. Note that some turns might arrive out of order or have missing timestamps.
#Data Structures
#Sorting
#Edge Cases
Data Engineer
•
Coding
•
hard
Write a distributed map-reduce job from scratch in Python using multiprocessing to count token frequencies across multiple files.
#Python
#Multiprocessing
#MapReduce
#Concurrency
Data Engineer
•
Coding
•
medium
Write a script to sample exactly K random lines from a massive text file in a single pass.
#Probability
#Reservoir Sampling
#Big Data
Data Engineer
•
Coding
•
medium
Implement an LRU cache with a TTL (Time To Live) for caching database queries.
#Data Structures
#Hash Maps
#Linked Lists
#Caching
Data Engineer
•
Coding
•
medium
Given a list of data pipeline tasks with dependencies, write a function to return a valid execution order.
#Graphs
#Topological Sort
#DAGs
Data Scientist
•
Coding
•
hard
Given a stream of incoming API requests represented as tuples of (timestamp, user_id, token_count), write a Python algorithm to identify users who are consistently hitting the 99th percentile of token usage within any rolling 5-minute window.
#Streaming Data
#Sliding Window
#Heaps/Queues
Data Scientist
•
Coding
•
medium
Write a Python function to parse a massive JSONL file of ChatGPT conversation logs (too large to fit in memory) and compute the rolling 7-day average of messages per session.
#Data Generators
#Memory Management
#Time Series
Data Scientist
•
Coding
•
hard
Implement a stratified sampling algorithm in Python to select prompt-response pairs for human evaluation (RLHF), ensuring proportional representation across 50 languages and 20 topic categories.
#Sampling
#Probability
#Data Structures
Data Scientist
•
Coding
•
medium
Given a list of user sessions containing timestamps and generated token counts, write an algorithm in Python to classify sessions as 'bot/scraper' vs. 'human' based on generation cadence and prompt frequency.
#Anomaly Detection
#Time Series
#Python
DevOps Engineer
•
Coding
•
medium
Write a function to check if a given CIDR block overlaps with a list of existing CIDR blocks in a VPC.
#Networking
#Bit Manipulation
#IP Addressing
DevOps Engineer
•
Coding
•
medium
Write a script to parse a massive, 500GB log file to find the top 10 IP addresses making requests, optimized for memory constraints.
#File I/O
#Data Structures
#Memory Management
#Streaming
DevOps Engineer
•
Coding
•
medium
Implement a token bucket rate limiter in Go or Python that can be used across a distributed system.
#Concurrency
#Distributed Systems
#Redis
DevOps Engineer
•
Coding
•
medium
Given a list of server dependencies (e.g., A depends on B, B depends on C), write a script to determine the correct startup order.
#Graphs
#Topological Sort
#DFS/BFS
DevOps Engineer
•
Coding
•
hard
Write a concurrent Go program (or Python with asyncio) to ping 10,000 endpoints and return a list of unreachable ones within a strict 5-second timeout.
#Concurrency
#Networking
#Goroutines
#Asyncio
DevOps Engineer
•
Coding
•
medium
Implement a basic load balancer in Python that distributes incoming requests to a list of backend servers using a weighted round-robin algorithm.
#Load Balancing
#Math
#Data Structures
Frontend Engineer
•
Coding
•
medium
Write a function to deeply merge two JavaScript objects. It should handle nested objects, arrays, and edge cases like null or undefined.
#Recursion
#Data Structures
#Type Checking
Frontend Engineer
•
Coding
•
hard
Write a function to parse and render a continuous stream of Markdown text. How do you handle incomplete Markdown tokens (e.g., a code block that has started with '```' but hasn't closed yet)?
#Parsing
#String Manipulation
#Edge Cases
Frontend Engineer
•
Coding
•
medium
Write a function that takes a string of HTML and returns true if the tags are properly balanced and nested, and false otherwise.
#Stacks
#String Parsing
#Regex
Frontend Engineer
•
Coding
•
medium
Implement an LRU (Least Recently Used) Cache class in JavaScript. It should have `get(key)` and `put(key, value)` methods, both operating in O(1) time complexity.
#Data Structures
#Hash Maps
#Linked Lists
Frontend Engineer
•
Coding
•
easy
Write a function to traverse the DOM tree starting from a given node and return an array of all text nodes that match a specific regular expression.
#DOM API
#Tree Traversal
#Recursion
Frontend Engineer
•
Coding
•
hard
Implement a function that schedules tasks with a maximum concurrency limit. It should take an array of functions (returning promises) and a concurrency number.
#Promises
#Concurrency
#Queues
Frontend Engineer
•
Coding
•
medium
Write a function to find the shortest path between two DOM elements in the DOM tree (i.e., finding their lowest common ancestor and the path to it).
#DOM API
#Tree Traversal
#Pointers
Frontend Engineer
•
Coding
•
hard
Write a function to serialize a DOM tree into a JSON object, and another function to deserialize that JSON object back into a DOM tree.
#DOM API
#Serialization
#Recursion
Full Stack Engineer
•
Coding
•
medium
Implement an LRU cache with a time-to-live (TTL) feature. If an item expires, it should not be returned, and it should be evicted.
#Data Structures
#Hash Map
#Linked List
Full Stack Engineer
•
Coding
•
hard
Implement a simplified Byte Pair Encoding (BPE) token counting algorithm that calculates the number of tokens in a given string based on a provided vocabulary dictionary.
#Strings
#Greedy Algorithms
#NLP
Full Stack Engineer
•
Coding
•
medium
Implement a concurrent task runner in TypeScript that processes an array of async tasks but limits the maximum number of active promises to a given concurrency limit.
#TypeScript
#Promises
#Concurrency
Full Stack Engineer
•
Coding
•
easy
Given a raw text string representing a conversation, parse it into a structured JSON format of roles (system, user, assistant) and content blocks.
#String Manipulation
#Parsing
#Regex
Full Stack Engineer
•
Coding
•
medium
Design a function to merge overlapping text highlights in a document. Given an array of intervals [start, end], return an array of non-overlapping intervals.
#Arrays
#Sorting
#Intervals
Machine Learning Engineer
•
Coding
•
hard
Implement the Aho-Corasick algorithm to efficiently search for a large dictionary of toxic words within a streaming text generation output.
#Trees
#Trie
#String Matching
Machine Learning Engineer
•
Coding
•
medium
Write a Byte-Pair Encoding (BPE) tokenizer from scratch. Given a corpus of text and a target vocabulary size, implement the training and tokenization functions.
#String Manipulation
#Data Structures
#NLP
Machine Learning Engineer
•
Coding
•
hard
Implement an autoregressive generation loop with KV Caching. Assume a simplified transformer block is provided.
#Memory Management
#Transformers
#PyTorch
Machine Learning Engineer
•
Coding
•
medium
Implement a simplified Byte Pair Encoding (BPE) tokenizer. Given a corpus of text and a target vocabulary size, write a function to find the most frequent adjacent pair of characters or tokens and merge them.
#Strings
#Hash Maps
#NLP
Machine Learning Engineer
•
Coding
•
hard
Write a simple Autograd engine for scalar values from scratch. Implement the forward and backward passes for addition and multiplication.
#Calculus
#Graphs
#Object-Oriented Programming
Machine Learning Engineer
•
Coding
•
medium
Design a data structure for efficient KV cache eviction in an LLM serving engine. It must support O(1) inserts, O(1) lookups, and evict the least recently used sequence block.
#Data Structures
#Linked Lists
#Hash Maps
Machine Learning Engineer
•
Coding
•
hard
Write a function to perform matrix multiplication of two large 2D arrays. Optimize it for cache locality using block matrix multiplication (tiling).
#C++
#Performance Optimization
#Computer Architecture
Machine Learning Engineer
•
Coding
•
medium
Implement Beam Search decoding for a language model given a function that returns the next-token probabilities.
#Search Algorithms
#Heuristics
#NLP
Machine Learning Engineer
•
Coding
•
medium
Implement a Token Bucket rate limiter for the OpenAI API. It needs to handle multiple users, support concurrent requests, and be highly performant.
#Concurrency
#System Design
#Data Structures
Machine Learning Engineer
•
Coding
•
medium
Given a Directed Acyclic Graph (DAG) representing a computation graph of ML operations, write an algorithm to schedule the operations on a fixed number of parallel workers to minimize total execution time.
#Graphs
#Scheduling
#Topological Sort
Machine Learning Engineer
•
Coding
•
hard
Implement a mock distributed parameter server. Write the worker code that computes gradients and the server code that aggregates them and updates weights, communicating via queues.
#Concurrency
#Distributed Systems
#Python
Machine Learning Engineer
•
Coding
•
medium
Given a list of text highlight spans (start_index, end_index) from multiple human labelers, write a function to merge all overlapping spans into a consolidated list of highlighted regions.
#Arrays
#Sorting
Software Engineer
•
Coding
•
medium
Implement a rate limiter for the OpenAI API that restricts users based on both requests per minute (RPM) and tokens per minute (TPM).
#Data Structures
#Concurrency
#API Design
Software Engineer
•
Coding
•
medium
Implement a function that takes a string and a list of forbidden words, and redacts the forbidden words in O(N) time.
#Trie
#Aho-Corasick
#String Matching
Software Engineer
•
Coding
•
medium
Write a script to efficiently sample from a probability distribution of logits given a specific temperature parameter.
#Math
#Probability
#Arrays
Software Engineer
•
Coding
•
medium
Write an algorithm to find the longest common substring between two large text documents to detect potential training data memorization.
#Dynamic Programming
#Suffix Trees
#Rolling Hash
Software Engineer
•
Coding
•
hard
Implement a streaming JSON parser that yields valid JSON objects as chunks of characters arrive over a network.
#Parsing
#State Machines
#Streaming
Software Engineer
•
Coding
•
medium
Merge K sorted streams of training data efficiently, assuming the streams are too large to fit into memory.
#Heaps
#External Sorting
#Pointers
Software Engineer
•
Coding
•
medium
Write an async Python script to fetch data from multiple endpoints, aggregate the results, and handle timeouts or partial failures gracefully.
#API Integration
#Asynchronous Programming
#Error Handling
Software Engineer
•
Coding
•
hard
Implement a sliding window attention mechanism algorithm that computes attention scores only for the last K tokens.
#Sliding Window
#Arrays
#Math
Software Engineer
•
Coding
•
medium
Find the shortest path in a Directed Acyclic Graph (DAG) representing a neural network computation graph to optimize memory allocation.
#Graphs
#Topological Sort
#Dynamic Programming
Software Engineer
•
Coding
•
hard
Implement a distributed task queue in Python using asyncio, supporting task priorities, retries with exponential backoff, and concurrency limits.
#Asynchronous Programming
#Heaps
#System Design
Software Engineer
•
Coding
•
medium
Write a function to perform matrix multiplication efficiently, then explain how you would optimize it for CPU cache locality.
#Math
#Memory Management
#Optimization
Software Engineer
•
Coding
•
medium
Given a list of API requests with start and end timestamps, find the maximum number of concurrent requests at any point in time.
#Arrays
#Sorting
#Sweep Line Algorithm
Software Engineer
•
Coding
•
hard
Write a streaming JSON parser that can handle incomplete JSON strings, similar to processing chunks generated sequentially by an LLM.
#Parsing
#State Machines
#String Manipulation
Software Engineer
•
Coding
•
medium
Design a thread-safe rate limiter using the Token Bucket algorithm to be used across a distributed API cluster.
#Concurrency
#Distributed Systems
#Data Structures
Software Engineer
•
Coding
•
hard
Implement a simplified version of Byte Pair Encoding (BPE) tokenization from scratch given a vocabulary and a text string.
#String Manipulation
#Greedy Algorithms
#Data Structures
Software Engineer
•
Coding
•
hard
Given a directed acyclic graph (DAG) representing dependencies of training jobs, write a function to execute them in the correct order concurrently.
#Graphs
#Topological Sort
#Concurrency
Software Engineer
•
Coding
•
medium
Design a data structure that supports insert, delete, and getRandom in O(1) time.
#Data Structures
#Hash Maps
#Arrays
Software Engineer
•
Coding
•
medium
Given a string of text, write a function to reverse the order of words, but keep the punctuation in its original relative position.
#Strings
#Two Pointers
Software Engineer
•
Coding
•
hard
Write a C++ program to efficiently multiply two large matrices, optimizing for CPU cache locality.
#C++
#Performance Optimization
#Computer Architecture
Software Engineer
•
Coding
•
hard
Implement a distributed task queue for scheduling model evaluation jobs across a cluster of workers.
#Distributed Systems
#Concurrency
#Queues
Software Engineer
•
Coding
•
medium
Implement a Trie data structure for fast prefix matching to filter out blocked or policy-violating prompt keywords.
#Trees
#Strings
#Safety
Software Engineer
•
Coding
•
medium
Merge K sorted arrays, representing log files from distributed training nodes, into a single sorted output.
#Heaps
#Sorting
#Distributed Systems
Software Engineer
•
Coding
•
medium
Implement an LRU Cache with a Time-To-Live (TTL) feature. If an item is expired, it should not be returned.
#Data Structures
#Caching
Software Engineer
•
Coding
•
medium
Write a Python async function to fetch data from multiple endpoints concurrently, with a strict timeout and exponential backoff retry logic.
#Python
#Asyncio
#Networking
Software Engineer
•
Coding
•
medium
Design a thread-safe rate limiter for the OpenAI API that can handle burst traffic and different tier limits (e.g., Free vs. Pro users).
#Concurrency
#System Design
#Data Structures
Software Engineer
•
Coding
•
hard
Implement a basic Byte-Pair Encoding (BPE) tokenizer from scratch given a corpus of text.
#Strings
#Data Structures
#NLP
Software Engineer
•
Coding
•
medium
Find the longest substring with at most K distinct characters. (Analogy: optimizing a context window for specific entity types).
#Sliding Window
#Strings
#Hash Maps
Software Engineer
•
Coding
•
medium
Write an algorithm to efficiently merge multiple sorted streams of log data (timestamped events) from thousands of different GPU nodes into a single chronological stream.
#Heaps
#Sorting
#Distributed Data
Software Engineer
•
Coding
•
medium
Implement a text justification algorithm optimized for streaming chunks of text as they are generated by an LLM, ensuring the UI updates smoothly without jarring reflows.
#String Manipulation
#Streaming Data
#UI/UX considerations
Software Engineer
•
Coding
•
easy
Given a stream of API request logs containing user_id, timestamp, and token_count, write a function to calculate the monthly billing per user based on a tiered pricing model.
#Data Processing
#Math
#Hash Maps
Software Engineer
•
Coding
•
hard
Implement a concurrent web crawler to fetch web pages for building an LLM training dataset. The crawler must respect robots.txt, handle domain-level rate limits, and avoid memory overflow.
#Concurrency
#Graph Traversal
#System Resources
Software Engineer
•
Coding
•
medium
Write a function to perform a simplified Byte-Pair Encoding (BPE) tokenization on a given string, given a vocabulary of base characters and a list of merge rules.
#String Manipulation
#Greedy Algorithms
#Hash Maps
Difficulty Radar
Based on recent AI-sourced data.
Meet Your Interviewers
The "Standard" Interviewer
Senior EngineerFocuses on core competencies, system constraints, and clear communication.
SimulateUnwritten Rules
Think Out Loud
Always explain your thought process before writing code or drawing architecture.