Project deep dive: present a project you ledBehavioralPresent a project you led in about 20 minutes: context, your role, the architecture, three hard trade-offs, metrics, cost and return, and what you would change. Then take 25…
Last asked Sep 2026
Google first round: coding interview
Round 3 of 8 · 146 questions reported
- Length
- 45 min
- Format
- Coding in a Google Doc, no syntax highlighting or autocomplete
- They grade
- Dialogue, complexity analysis and edge cases; bug-free code is not required
- AI use
- No AI
Questions Google asks in this round 146
- Trie with insert, search and prefix lookupCodingBuild a trie over a dictionary of words. Support inserting a word, checking whether an exact word is present, and returning every word that starts with a typed prefix, as an…Last asked Jul 2026
- Most active user by distinct contacts, then top KCodingUsers send each other messages, and a message between A and B counts as contact for both of them. Build a class with: - register(a, b): record a message between a and b. -…Last asked Sep 2026
- Expand placeholders from a variable storeCodingImplement a small store of variables, like the export NAME="Tom" lines of a shell startup file. Any string can refer to a variable as %NAME%; expanding the string replaces each…Last asked Sep 2026
- Sliding window average excluding the k largestCodingImplement windowedaverages(nums, windowsize, k). Slide a window of windowsize consecutive elements across the integer array nums, from left to right. For each full window, drop…Last asked Sep 2026
- Count clusters of 2D points within a radiusCodingTwo points belong to the same cluster when they are within a given distance of each other, and clusters chain through shared neighbors. Given the points and the distance, count…Last asked Jul 2026
- Reach a target when you can only step between nearby pointsCodingYou get a set of unordered points, a start point, an end point, and a function getDistance(x, y). You can step from one point to another only when their distance is within a…Last asked Jul 2026
- Monotone increasing digitsCoding1. Check whether a number's digits never decrease from left to right. 2. Given n, return the largest number no greater than n whose digits never decrease.Last asked Jul 2026
- Greedy longest-match tokenizerCodingImplement a greedy longest-match tokenizer. You are given a string text and a list dictionary. Each entry has the form "<key:<id". key is a non-empty token string and id is its…Last asked Jun 2026
- Which interval contains a number?CodingBuild a class with addNonOverlappingInterval(start, end) and a query that says whether a number falls inside a stored interval (and which one). Discuss three versions: a linear…Last asked Jun 2026
- Snake case to camel case, then across a whole repositoryCoding1. Convert a valid snakecase name (no leading, trailing or doubled underscores) to lowerCamelCase, so foobar becomes fooBar. 2. An open discussion: a huge repository names its…Last asked Apr 2026
- Is every 3+ letter piece of a string a dictionary word?Coding1. Given a string and a dictionary, return true when every piece of the string of length 3 or more is a valid word. (The report says subsequences; confirm with the interviewer…Last asked Mar 2026
- Fewest deletions so a list's first k items avoid another listCodingYou get two lists, a and b, and an integer k. Delete elements from b so that none of the first k elements of what remains also appears in a. Return the fewest deletions needed (or…Last asked Feb 2026
- Minimum servers for daily jobs that wrap past midnightCodingEach job runs every day over a time window on a 24-hour clock, and a window may wrap past midnight (start later than end). A server runs one job at a time. Return the fewest…Last asked Feb 2026
- Grid path that keeps its highest cell as low as possibleCodingEach cell of an m x n grid holds a height. Find a path from the top-left to the bottom-right cell, moving up, down, left or right, whose highest cell is as low as possible, and…Last asked Feb 2026
- Present and defend your researchBehavioralA research-focused conversation with no coding. Introduce your research (or dissertation) briefly, then answer detailed follow-up questions on your methods and results: what you…Last asked Jan 2026
- Distance from every cell to the nearest taxiCodingA grid marks the cells where taxis are parked. Return, for every cell, the distance to the nearest taxi (moving up, down, left or right). Use a multi-source BFS and say why it…Last asked Jan 2026
- Lowest horizontal line that splits squares into equal areasCodingSeveral axis-aligned squares are given by their bottom-left corner and side length. Find the lowest horizontal line y = h such that the total square area below the line equals the…Last asked Jan 2026
- Meeting rooms with delayed starts: the busiest roomCodingThere are n rooms numbered from 0 and a list of meetings with distinct start times. Each meeting takes the free room with the lowest number; if none is free, it waits for the…Last asked Jan 2026
- Range queries: is the subarray parity-alternatingCodingCall an array special when every pair of neighbouring elements has different parity (one odd, one even). Given an integer array and many queries from, to, answer for each query…Last asked Jan 2026
- Shortest subarray with at least k distinct valuesCodingYou are given an integer array arr and an integer k. Call a contiguous subarray good if it contains at least k different values. Return the length of the shortest good subarray…Last asked Jan 2026
- Design a feed recommendation systemML designRank the items in each user's home feed so they engage more, choosing from millions of candidates within a couple of hundred milliseconds.Last asked Dec 2025
- Fewest guesses in Wordle with green feedback onlyCodingA secret five-letter word must be found, and the only feedback is, for a guess, which positions hold the right letter. Design a guessing strategy that finds the word in as few…Possibly retired
- Design a Kafka-like distributed message queueSystem designDesign a durable, partitioned log that producers append to and many consumer groups read at their own pace, surviving broker failures without losing acknowledged messages.Possibly retired
- Design automated anomaly detection and remediation for cloud servicesML designDesign a platform that watches metrics and logs across many cloud services, detects anomalies, and responds automatically where it is safe (restart, roll back, scale) while paging…Possibly retired
- Shortest path that avoids blocked nodesCodingGiven an unweighted graph, a start node and a set of blocked nodes that cannot be entered, return the shortest distance from the start to every node (or to a given end node), with…Possibly retired
- Binary tree zigzag level-order traversalCodingReturn a binary tree's values level by level, alternating direction: left to right on the first level, right to left on the next, and so on. Use a BFS by levels and reverse (or…Possibly retired
- Log manager that evicts the least important logsCodingDesign a log manager that keeps at most totalmax logs. Each log has an importance; when a new log would go over the limit, the least important logs are deleted automatically…Possibly retired
- Disagreements with a coworker, another team and a menteeBehavioralThree behavioral questions in one round, each answered with a real story: what happened, what you did and how it ended. 1. You and a coworker disagreed about the work. How did you…Last asked Oct 2026
- Best value from unit-weight items with limited copiesCodingA bag holds at most capacity units of weight. There are n kinds of item; every copy of kind i weighs 1 and is worth valuesi, and there are countsi copies of it. Return the most…Last asked Oct 2026
- Merge two config trees with per-node merge rulesCodingTwo configuration files have been parsed from YAML into trees of dicts, lists and plain values: a base and an overlay. Merge the overlay into the base. Each node can carry its own…Last asked Oct 2026
- Median of several sorted arraysCodingYou get several integer arrays, each sorted in non-decreasing order. Return the median of all their values taken together. The interview started with exactly two arrays and then…Last asked Oct 2026
- Design an LLM agent for production status, work orders and quotesAI systemPeople at a manufacturing business talk to an AI agent in plain language. It has to handle three kinds of request: report how far along an order or production job is, open a new…Last asked Oct 2026
- Number of islands as land is addedCodingA grid starts as all water. Positions are turned into land one at a time; after each addition, return the current number of islands (land cells connected up, down, left or right)…Last asked Oct 2026
- Delete leaves with a target value, repeatedlyCodingGiven a binary tree and a target value, delete every leaf that holds the target. If that turns its parent into a leaf holding the target, delete the parent as well, and keep going…Last asked Sep 2026
- First missing positiveCodingGiven an unsorted list of integers that may include negatives, zeros, duplicates and values much larger than the list's length, return the smallest positive integer that does not…Last asked Sep 2026
- How would you verify a smile detector in a photo app?ML designYou are on the Google Photos team and your feature detects smiling faces in photos. How would you check that the detection is correct? Cover what counts as a smile and who decides…Last asked Sep 2026
- Tell me about a time you compromisedBehavioralTell me about a time you had to compromise. After the story, expect probes: how you will act differently because of that experience, whether you are satisfied with how it turned…Last asked Sep 2026
- Duplicate detection: sliding windows, then read-heavy queriesCodingStart with checking an array for duplicate values, then evolve the solution step by step: first find duplicates that fall within a sliding window of positions, then rework the…Last asked Sep 2026
- Longest straight run of one color in a gridCodingGiven a grid of colors such as R, G and B, return the length of the longest line of cells with the same color, running horizontally, vertically or diagonally.Last asked Aug 2026
- Detect and prevent reward hackingML designExplain reward hacking when a language model is trained with reinforcement learning: what it looks like, how you would detect it, and what you would change in the reward, the data…Last asked Aug 2026
- Importance sampling in LLM trainingML designExplain importance sampling: what it is and why it works. Then explain where it is used when training large language models and why it is used there. Expect to go beyond the…Last asked Aug 2026
- KL divergence in language modelsML designDefine KL divergence and explain what it measures. Then explain where it is used with large language models and why, for example as a penalty that keeps a fine-tuned model close…Last asked Aug 2026
- Pipeline parallelism in GRPO trainingML designExplain pipeline parallelism and how it applies when a language model is trained with GRPO: how the model is split into stages across devices, how micro-batches keep the stages…Last asked Aug 2026
- Reusable locker allocation systemCodingBuild a system that hands out lockers and takes them back so they can be used again: assign a free locker on request, release it later, and keep both operations fast as the number…Last asked Aug 2026
- Reward-model RLHF versus direct preference optimizationML designWalk through a classic RLHF pipeline: supervised fine-tuning, a reward model trained on preference pairs, then policy optimization (PPO) with a KL penalty to the reference model…Last asked Aug 2026
- VAEs: the ELBO, the KL term and reparameterizationML designDefine a variational autoencoder and its evidence lower bound (ELBO). Why does the objective include a KL divergence term, and what does it do? Explain the reparameterization…Last asked Aug 2026
- What perplexity tells you about a language modelML designDefine perplexity and explain how to read it: what a lower or higher number means, how it relates to cross-entropy, how it is used for today's large language models, and where it…Last asked Aug 2026
- Design a music recommender driven by an LLM agentAI systemDesign a music recommendation product in which an LLM agent talks with the listener and suggests songs or playlists. Cover how the agent reaches the listener's history and the…Last asked Aug 2026
- Design permission-aware enterprise searchAI systemDesign search across every app a company uses (Drive, Confluence, Slack, Jira, GitHub, email and more) from one search box, plus an assistant that answers from the results. Nobody…Last asked Aug 2026
- Count simple paths whose labels match a prefixCodingEvery node of a graph carries a label. Count the simple paths (paths that never repeat a node) whose sequence of labels matches a given prefix string. Explain how you prune the…Last asked Aug 2026
- Check a new interval against existing ones for conflictsCodingGiven a set of existing intervals, decide whether a new interval overlaps any of them. Then discuss answering many such checks quickly as intervals keep being added, for example…Last asked Aug 2026
- Lazy tee iteratorCodingImplement tee in Python: from one source iterator, create n independent iterators that each yield the full sequence. Pull from the source only when some copy needs the next item…Last asked Aug 2026
- Count visible people in a lineCodingPeople stand in a line and heightsi is the height of the person at position i. Two people can see each other when nobody standing between them is taller than both of them. First…Last asked Jul 2026
- Design a scalable, safe agentic systemAI systemDesign an agent system and talk through its problems with the interviewer: how it extends to more tools and tasks, how you keep its actions safe, and what you do when an agent…Last asked Jul 2026
- Build your own CompletableFutureCodingImplement a small version of CompletableFuture: a result that some thread completes later, that other threads can wait on, and that can be chained with callbacks. Then use it to…Last asked Jun 2026
- Design a video generation service on a scarce GPU poolAI systemUsers submit text-to-video requests that each need minutes of GPU time, and the GPU pool is limited and changes size. Design the request flow, scheduling and workers, how users…Last asked Jun 2026
- Threshold infection spread on a gridCodingA lab tracks a disease across a rectangular field of cells. You are given an m x n grid where 0 is a healthy cell and 1 is an infected cell, and an integer threshold. Each day…Last asked Jun 2026
- Horizontal line that splits the area of rectangles in halfCodingGiven axis-aligned rectangles, find the lowest horizontal line y = c for which the total rectangle area above the line equals the total area below it. Discuss how overlapping…Last asked Jun 2026
- Design a quota serviceSystem designTrack and enforce how much of each resource (API calls, storage, compute) every tenant may use, with fast checks and limits that stay accurate across regions.Last asked May 2026
- Design a security monitoring frameworkSystem designDesign a framework that collects security signals such as logs and events from many systems, detects suspicious activity, raises alerts and supports investigations. Cover…Last asked May 2026
- Game of Life, updated in placeCodingEach cell of a grid is alive or dead, and all cells update together from the states of their eight neighbors, as in Conway's Game of Life. Compute the next state in place, without…Last asked May 2026
- Turnstile crossing timesCodingPeople arrive at a single turnstile at given times, each wanting to enter or to exit, and one person passes per second. When people going both ways are waiting, a priority rule…Last asked May 2026
- Can one board be turned into another by moving pieces?CodingA board is a string of R, L and empty cells. R pieces can only move right and L pieces only left, one empty cell at a time, and no piece can jump over another. Decide whether a…Last asked Apr 2026
- Helping a struggling peer, and your greatest achievement outside workBehavioralA behavioral round with common and less common questions: how you helped a peer who was underperforming, your most challenging project, and your greatest achievement outside of…Last asked Apr 2026
- Cold start in ranking systemsML designHow do you rank new items or serve new users that have no interaction history? Discuss content features, exploration, priors and boosting, how to move from cold to warm signals…Last asked Mar 2026
- Substring search and weighted random samplingCodingTwo problems for a machine learning engineer screen: 1. Find where a pattern occurs in a text, and discuss doing better than checking every position. 2. Pick an item at random…Last asked Mar 2026
- Palindrome number and merge intervalsCodingTwo short problems: 1. Decide whether an integer reads the same forwards and backwards. 2. Merge a list of possibly overlapping ranges into the fewest non-overlapping ranges.Last asked Mar 2026
- CPU microarchitecture and simulator designCodingFor a CPU architect role: read and reason about assembly code; explain microarchitecture parts such as branch predictors, the MOESI coherence protocol, caches and MSHRs, VIPT…Last asked Mar 2026
- Russian doll envelopesCodingEach envelope has a width and a height. One fits inside another when both its width and height are strictly smaller. Return the largest number of envelopes you can nest one inside…Last asked Mar 2026
- Is a 14-tile mahjong hand a winning hand?CodingGiven 14 mahjong tiles, decide whether they form a winning hand: four sets, each three identical tiles or three consecutive tiles of the same suit, plus one pair.Last asked Mar 2026
- Design a replay system for publish-subscribeSystem designPublishers send messages to subscribers through a pub-sub system. Design a replay feature that lets a subscriber receive past messages again from a chosen point. Cover how…Last asked Mar 2026
- Two teams working on the same projectBehavioralWhat do you do when you find out two teams are working on the same project? Explain how you would raise it, who decides, and how you keep both teams' work from going to waste.Last asked Mar 2026
- Probability of landing in a range on a dice walkCodingYou start at position 0 on an endless line. Each turn you roll a die with faces 1 to K and move forward that many steps. You win if you finish inside the range mn, mx, and lose…Last asked Mar 2026
- A teammate who feels pressured by your paceBehavioralA teammate who usually coasts tells you that how hard you work puts a lot of pressure on them. What do you do?Last asked Feb 2026
- Manager and peer relationships with is_manager queriesCodingImplement three functions: - manager(a, b): a is the manager of b. - peer(a, b): a and b have the same manager. - ismanager(a, b): return whether a is a manager of b. Decide how…Last asked Feb 2026
- Fewest boards to cover every hole in a roofCodingA roof has holes at given positions along a line, and boards of a fixed length can be laid over it. Return the fewest boards needed so every hole is covered. Sort the holes and…Last asked Feb 2026
- LLM fine-tuning and generative modelsML designExplain how large language models are fine-tuned: supervised fine-tuning, parameter-efficient methods such as LoRA, and preference tuning, with the trade-offs of each. Then…Last asked Feb 2026
- Shortest relationship path between two peopleCodingPeople are linked by relationships (a graph where each edge is a direct relationship). Given two people, return the shortest chain of relationships that connects them, or say that…Last asked Feb 2026
- Top K frequent elements and K closest pointsCodingTwo warm-up style problems that the interviewer combined into one round: 1. Return the k points closest to the origin. 2. Return the k most frequent values in a list. Then combine…Last asked Feb 2026
- Check that a parent array forms a valid treeCodingYou get an array where parenti is the parent of node i (the root has no parent, for example -1). Return whether the array describes one valid tree: exactly one root, no cycles…Last asked Feb 2026
- Crack a 4-digit code from exact-match countsCodingA server holds a secret 4-character code. Each character is a digit from '0' to '9'. Digits may repeat, and the code may start with zeros. You can only learn about the code…Last asked Feb 2026
- Design app recommendations for an app storeML designRecommend apps to each user on an app store's home page and in its search results. Cover candidate generation and ranking, the signals you would use (installs, uninstalls, usage…Last asked Feb 2026
- Waitlist with top-K and bottom-K queriesCodingBuild a waitlist. People join with a priority (or a join time), can leave, and the system answers two queries at any moment: the top k entries and the bottom k entries. Choose…Last asked Feb 2026
- Design layer document with undo, redo and batchesCodingYou are building the core of a design tool. A document holds layers. Each layer has a unique integer id and a set of string properties, such as color, shape or size. A layer does…Last asked Feb 2026
- Host several websites on one server with one public IPSystem designYou have one server and one public IP address, and three small businesses each want their own website at their own domain. Explain how to serve all three from that machine, then…Last asked Feb 2026
- What happens when you run lsCodingWalk through what happens, from the shell down to the kernel, when you type ls in a terminal and press Enter: how the shell finds and starts the program, the system calls…Last asked Feb 2026
- Decide whether two people in a family tree are relatedCodingYou get a family tree as parent and child links. Given two people in it, decide whether they are related through the tree. Agree on what "related" means with the interviewer (for…Last asked Jan 2026
- Design a payment fraud detection systemML designScore every card payment for fraud within tens of milliseconds, balancing blocked fraud against declined good customers, with labels that arrive weeks later.Last asked Jan 2026
- Design a street-level imagery ingestion and storage systemSystem designVehicles capture large volumes of street-level photos. Design how the images are uploaded, processed, stored and served: ingestion from the field, metadata such as location and…Last asked Jan 2026
- Sum of distances from every node in a treeCodingGiven an undirected tree with n nodes, return for every node the sum of its distances to all other nodes. A BFS from every node is too slow; compute it in linear time with two…Last asked Jan 2026
- Top-k and bottom-k words in a list and in a streamCoding1. Given a list of words, return the k most frequent and the k least frequent. 2. Now the words arrive as a stream: keep both answers available at any moment. 3. Discuss how to…Last asked Jan 2026
- Fast expensive tokens versus slow cheap tokensAI systemAn LLM provider offers fast but expensive tokens and slow but cheap ones. How would you decide which to use for a product? Discuss which features need low latency, batch versus…Last asked Jan 2026
- K largest subset sumsCodingYou get n items with non-negative weights. Return the k largest subset sums, in decreasing order (subsets are distinct by the items they contain). Brute force over all subsets is…Last asked Jan 2026
- Design a hit counterCodingImplement a counter with hit(timestamp) and gethits(timestamp), where gethits returns the number of hits in the last five minutes. Timestamps arrive in order. Follow-ups: many…Last asked Jan 2026
- Fastest trip when two travellers may meet and ride togetherCodingTwo people start at different nodes of a graph and both need to reach the same destination. They may travel separately, or meet at some node and take the bus together from there…Last asked Jan 2026
- Iterator that yields one array first, then the rest of anotherCodingDesign an iterator over two integer arrays, a and b, that returns elements in this order: 1. Every element of b, in its original order (duplicates included). 2. Then every element…Last asked Jan 2026
- Logger that reports its top K messagesCodingBuild a logger that receives messages over time and can return the k most frequent messages at any point. Choose structures so logging stays fast and the top-K query is efficient…Last asked Jan 2026
- Longest strictly increasing contiguous subarrayCodingReturn the length of the longest contiguous subarray whose elements strictly increase. Solve it in one pass and constant extra space, then discuss variants such as returning the…Last asked Jan 2026
- Maximum sum of non-adjacent houses, on a line, a circle and a treeCodingEach house holds some value and you cannot take two neighbours. Find the best total for houses in a row, then for houses arranged in a circle, then for houses arranged as a binary…Last asked Jan 2026
- Median of two run-length encoded arraysCodingTwo sorted arrays are given in run-length form (value and count pairs). Return the median of all their values combined, without expanding the runs. Explain how binary search on…Last asked Jan 2026
- Winner of a stack-merging gameCodingTwo players take turns merging stacks according to the game's rules until no move is left. Given the starting stacks, decide which player wins if both play optimally. Start with a…Last asked Jan 2026
- Recover the original array from its doubled shuffleCodingAn array was built by taking an original array, appending twice each of its values, and shuffling the result. Given the shuffled array, return the original, or an empty result if…Last asked Jan 2026
- Set with constant-time insert, delete and get randomCodingDesign a set with add, remove and getrandom, all in average O(1); getrandom returns each element with equal probability. Handle empty-set and missing-element cases. Follow-up: how…Last asked Jan 2026
- Match people to questions using tags and prioritiesCodingPeople have skill tags and questions have tags and priorities. Assign questions to people so each question goes to someone whose tags fit, higher-priority questions are served…Last asked Dec 2025
- Most deliveries on a line within a distance limitCodingDelivery points lie on a number line and the courier may travel at most a given distance. Choose deliveries to complete as many as possible, and among the best choices, minimise…Last asked Dec 2025
- Concurrent same-host web crawlerCodingImplement a web crawler that finds every page reachable from a start URL on the same host, and fetches pages concurrently. You are given a blocking helper: Write: python def…Last asked Dec 2025
- Implement a transformer block with SwiGLUCodingWrite a transformer block from scratch: multi-head self-attention, the residual connections and normalisation, and a feed-forward layer that uses the SwiGLU gate (two parallel…Last asked Dec 2025
- Design the ML system for self-driving perceptionML designDesign the perception system of a self-driving car: which sensors feed it, which models detect and track objects, how training data is collected and labelled, how you evaluate…Last asked Dec 2025
- GRPO-style reinforcement learning for diffusion modelsML designExplain how a group-relative policy optimisation method (GRPO) works for language models, then how you would adapt it to fine-tune a diffusion model against a reward: what counts…Last asked Dec 2025
- Longest duplicated substringCodingReturn any longest substring that occurs at least twice in a string (the occurrences may overlap), or an empty string if none does. Binary search on the length with a rolling…Last asked Dec 2025
- Maximum value in a file too big for memoryCodingA very large text file holds one number per line. Return the largest value. Then speed it up: split the file into chunks, find each chunk's maximum in parallel, and combine. Write…Last asked Dec 2025
- Shuffle an array with a random-integer functionCodingUsing only a function that returns a uniform random integer in a range, shuffle an array (for example a deck of cards) so every permutation is equally likely. Implement…Last asked Dec 2025
- The skyline problemCodingBuildings are given as left, right, height rectangles on flat ground. Return the outline of the skyline they form, as the list of key points where the height changes. Use a sweep…Last asked Dec 2025
- Top K most active users from chat logsCodingYou get chat log lines, each naming the users involved. Return the k users who took part in the most chats. Count with a hash map, then compare picking the top k by sorting, by a…Last asked Dec 2025
- Add two big integers stored as digit listsCodingTwo non-negative integers too large for built-in types are given as lists of digits. Return their sum in the same form. Handle different lengths and the final carry, and say how…Last asked Nov 2025
- Count single-colour squares in a character gridCodingEach cell of a grid holds a character standing for a colour. Count all square sub-grids whose cells all have the same colour, of every size. Use the DP where each cell stores the…Last asked Nov 2025
- Safe ranges between planets' gravity zonesCodingPlanets sit on a line; each is given as (center, radius) and makes the range within its radius unsafe. Return the safe ranges between the unsafe zones, in order. Turn each planet…Last asked Nov 2025
- Mode of a ternary search treeCodingIn this tree each node has up to three children: the left subtree holds smaller values, the middle child equals the node's value, and the right subtree holds larger values. Return…Last asked Nov 2025
- Settle group trip expenses with the fewest transfersCodingFriends on a trip record payments: each record names the payer, the amount and the people it covered (the payer may be among them), split evenly. Compute each person's net…Last asked Nov 2025
- Objects seen on both days by at least two clientsCodingTwo log files, one per day, hold lines of timestamp, objectid, clientid. Return the object ids that appear on both days and were accessed by at least two different clients. Then:…Last asked Nov 2025
- Binary tree right side viewCodingReturn the values visible when you look at a binary tree from the right: the last node of each level, top to bottom. Follow-ups: the left side view, and both views in a single…Last asked Nov 2025
- Find K pairs with the smallest sumsCodingGiven two sorted arrays and k, return the k pairs (one number from each array) with the smallest sums. Start a min-heap with pairs formed from the first elements and push the next…Last asked Nov 2025
- Numbers that are a sum of two squares in exactly two waysCodingFind the numbers up to a limit that can be written as a^2 + b^2 in exactly two different ways (unordered, with the agreed rule on zero). Enumerate pairs efficiently, count…Possibly retired
- Allocate servers from a pool of mixed node typesCodingA pool holds servers of several node types. Requests ask for a number of servers of a given type; the allocator hands them out and takes them back on release. Design the class and…Possibly retired
- Design a distributed key-value storeSystem designStore and serve billions of keys with low latency, partitioned across machines and replicated to survive failures, with tunable consistency.Possibly retired
- Design a distributed task scheduler with dependenciesSystem designDesign a system that runs jobs made of tasks with dependencies between them, including long-running tasks. Cover how jobs and their dependency graphs are stored, how ready tasks…Possibly retired
- Design a high-throughput publish-subscribe event systemSystem designProducers publish events on topics and many subscribers receive the events they subscribed to. Design it for very high throughput: subscription management, fan-out, delivery…Possibly retired
- Design a key management serviceSystem designDesign a service that creates, stores and rotates encryption keys for other services and performs encrypt and decrypt calls for them. Cover how master keys are protected (hardware…Possibly retired
- Design a migration from a relational database to NoSQLSystem designA live service must move its data from a relational database to a NoSQL store without downtime. Design the migration: modelling the data for the new store, the initial bulk copy…Possibly retired
- Design a protocol for distributed transactionsSystem designA transaction must update data held by several independent services or shards, so that either all changes happen or none do. Design the protocol: how participants agree to commit…Possibly retired
- Design a watch history and resume-playback serviceSystem designRecord what each user watched and how far they got, so playback resumes at the right point on any device. Cover the API, how often progress is written, storage for a very large…Possibly retired
- Design an image sharing service that stores each file onceSystem designDesign a service where users upload, view, download and delete images, and identical images are stored only once, keyed by a content hash. Explain how metadata and blobs stay…Possibly retired
- Design school-to-guardian messaging with acknowledgmentsSystem designA school sends messages (announcements, alerts, notes about a student) to parents and guardians, who must acknowledge important ones. Design delivery over several channels…Possibly retired
- Design the APIs of an executable notebook serviceSystem designUsers write notebooks of code cells and run them on the server. Design the APIs for creating and saving notebooks and running cells, and the system behind them: isolated execution…Possibly retired
- Multiply two matrices across two GPUsML designMatrices A and B must be multiplied using two GPUs, with both matrices split between them. How do you partition the work (by rows, by columns, by blocks), what has to move between…Possibly retired
- Predict the reaction factor of two moleculesML designA dataset gives pairs of molecules and the reaction factor measured for each pair. Build a model to predict the reaction factor for new pairs. Walk through exploring the data…Possibly retired
- Split a file iterator into balanced line-aligned partsCodingSplit a large file into balanced parts for parallel workers without cutting lines in half: each part holds whole lines and the parts stay close in size. Reported on 1point3acres'…Possibly retired
- Validate a course catalog's prerequisitesCodingA course catalog lists each course and its prerequisites. Check that the catalog is valid: every prerequisite exists and there is no cycle, so all courses can be taken in some…Possibly retired
- Can left and right pieces slide into a target stringCodingA string holds pieces that can only move left, pieces that can only move right, blanks, and walls that nothing passes. Given a start and a target string, decide whether the start…Possibly retired
- Unique users per activity and average time on siteCodingEach record captures one user's action on a website, with the user, the activity and the time. Write code that returns the number of unique users for each activity and the average…Possibly retired
- Merge two sorted linked listsCodingMerge two sorted linked lists into one sorted list and return its head, reusing the existing nodes. Do it iteratively with a dummy head, then discuss the recursive version.Possibly retired
- Walk through a dashboard you built and improvedBehavioralDescribe a dashboard you built: who used it, where the data came from, the tools you used, how you found problems in it or in the data, and what you changed. Expect follow-ups on…Possibly retired
- Koko eating bananasCodingThere are piles of bananas and h hours. Each hour Koko eats up to k bananas from one pile. Return the smallest integer k that lets her finish every pile within h hours. Binary…Possibly retired
- Count index pairs with an even product and odd distanceCodingGiven an integer array, count pairs i < j where numsi numsj is even and j - i is odd. Avoid checking every pair: count even and odd values by index parity and combine.Possibly retired
- Number of islandsCodingGiven a binary matrix, return how many islands it has: groups of 1 cells connected up, down, left or right (diagonals don't connect).Possibly retired