Persistent key-value store with binary snapshotsCodingImplement an in-memory key-value store whose whole state can be saved to, and restored from, a storage medium that holds a single binary blob. You are given: Implement
Last asked Oct 2026
#object-oriented design
Is the store open? Hours with split shifts and overnight windowsCodingWrite a check that answers whether a store is open at a given moment, in Java. The schedule starts simple and gets richer step by step, and every earlier query must keep working…Last asked Oct 2026
+1Design a parking lotOO designModel a multi-floor parking lot with spot types for motorcycles, cars and trucks: park, unpark, find free spots, and charge by time.Last asked Oct 2026- Extensible chat app with command botsCodingImplement an in-memory chat app with one shared channel that people and bots post to. Users send text. Some messages are slash commands (/name arg ...), and bots can respond to…Last asked Oct 2026
- +1Design a chess gameOO designModel a two-player chess game: board, pieces and their moves, turns, check, checkmate and stalemate, and special moves like castling.Last asked Sep 2026
- Three-card showdown between two playersCodingDesign a two-player card game that uses a standard 52-card deck. Each card has a rank and a suit. From lowest to highest, the ranks are 2 3 4 5 6 7 8 9 10 J Q K A. The suits are C…Last asked Sep 2026
+1Task manager with user quotas and expiring assignmentsCodingBuild an in-memory TaskManager in four levels. Each level adds methods to the same class, and you move to the next level only after the current one passes. Every method takes an…Last asked Sep 2026
Customer support dispatcher for agents who take breaksCodingBuild the core of a dispatcher for a customer support team. Customers get in touch and wait. Human agents sign in, serve one request after another, and sometimes leave, even in…Last asked Sep 2026- +1Unix find command with pluggable filtersCodingImplement a small version of the Unix find command over an in-memory file system. The file system holds directories and files. Each file has a name and a size in bytes. Its…Last asked Sep 2026
- Extensible spreadsheet range aggregatesCodingDesign a spreadsheet API with getsum, getmax and getmin over a range of cells, where a cell holds either a value or a formula. Show how someone adds a new aggregate later without…Last asked Sep 2026
Link object tracks across two perception systemsCodingTwo perception systems, A and B, track the same objects around a vehicle independently, each with its own IDs, and each emits observations of its tracks over time. Implement an…Last asked Sep 2026- Checkout price engine with pluggable discountsOO designBuild the price engine for an e-commerce checkout. A cart holds line items (product id, unit price, quantity) and the customer has a tier, standard or premium. Apply discounts of…Last asked Sep 2026
- Design a shopping cart (object-oriented)OO designWrite a small, runnable object model for an online store's shopping cart in the language of your choice: adding products, the other everyday cart operations, and computing the…Last asked Sep 2026
- Design a pizza price calculatorOO designModel pizzas with sizes, crusts and toppings, plus deals and coupons, and compute the price of an order. Make it easy to add new toppings and promotions.Last asked Sep 2026
- Bookshelf with book CRUD and a stable bookmarkCodingDesign a bookshelf that supports adding, reading, updating and removing books, plus a bookmark that keeps pointing at the right book while books are added or removed around it.Last asked Aug 2026
- Rectangle board with remove-at-cell, batch remove and undoCodingBuild a RectangleBoard that holds axis-aligned rectangles on a grid of width columns and height rows. Cells use zero-indexed (x, y), where x is the column and y is the row. A…Last asked Aug 2026
Primary and secondary circuit breakers with failoverCodingA service reads from a primary backend and can fail over to a secondary backend (for example a leader database and a follower). Put a circuit breaker in front of each backend so…Last asked Aug 2026- +1Shuffle, deal and sort a four-player card handCodingYou are building the core of a four-player card game. Model a standard 52-card deck and implement the deal. Types to define - Suit: CLUBS, DIAMONDS, HEARTS, SPADES, in this order…Last asked Aug 2026
- +1Turn-based monster team battle simulatorCodingWrite a deterministic simulator for a turn-based battle between two ordered teams of monsters, and return the battle log and the result. python class Monster: name: str unique…Last asked Aug 2026
- +1Meeting room scheduler over a fixed set of roomsCodingImplement a MeetingScheduler for a fixed set of meeting rooms. Each room has a unique string ID. - MeetingScheduler(roomids: liststr) sets up the rooms. Room IDs are unique. -…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
Select table cells and set a colorCodingDesign a Table class for a whiteboard app. A table has a fixed number of rows and columns. A user selects part of the table and sets a color on everything selected. Every cell…Last asked Aug 2026
Payment command parser and state machineCodingBuild the parser and the object-oriented state machine behind a payment command interface. Every command line has the same fixed number of positions, with empty strings in the…Last asked Aug 2026- +1Recipe manager with ingredient searchCodingBuild an in-memory recipe book. Each recipe has a name, an ordered list of ingredients and an ordered list of steps. The work comes in two parts; finish part 1 before you start…Last asked Jul 2026
- Tic-tac-toe with K playersCodingImplement tic-tac-toe for k players on an n x n board. Players take turns placing their marks. However large the board is, a player wins as soon as they have three of their marks…Last asked Jul 2026
- Concurrent restaurant waitlist and seatingOO designDesign and code a restaurant's waitlist and seating: parties join the list, tables free up, and parties get seated. Keep it correct when many requests happen at the same time.Last asked Jul 2026
- Inherited permissions across teams, folders and filesCodingDesign a permission system for a workspace organized as a hierarchy of teams, folders, and files. - A team is a root. It can contain folders and files. - A folder sits inside a…Last asked Jul 2026
- +1Design a hotel booking system (object-oriented)OO designModel hotels, room types, rooms, bookings, guests and payments: search availability for dates, book, and cancel with a policy.Last asked Jun 2026
- +1Resumable iterators that save and restore their positionCodingDefine an iterator interface that can export its state and be resumed from it later. Implement it for a flat list, then for nested multi-dimensional lists, then across several…Last asked Jun 2026
- Design a snake gameOO designDesign the snake game in object-oriented code: the board, the snake, food, moving, growing, and detecting collisions.Last asked Jun 2026
- Design a library management systemOO designModel books, copies, members, loans, holds and fines for a library, with search and limits on loans per member.Last asked Jun 2026
- +3In-memory SQL table with filtering and multi-key sortingCodingBuild a small in-memory SQL-like database. You do not need to parse SQL text. Queries arrive as structured arguments. Implement SQLManager: - createtable(name: str, columns:…Last asked May 2026
- +1Design a voting systemOO designModel polls with options, voters and ballots: cast one vote per voter, change it before closing, and tally results.Last asked May 2026
- Extensible cinema ticket pricing engineOO designDesign a ticket pricing engine for a cinema, built so that new pricing rules can be added later without rewriting the engine.Last asked May 2026
- +2Design an elevator control systemOO designModel a bank of elevators: hall and car requests, a dispatching strategy, direction and door states, and capacity limits.Last asked Apr 2026
- In-memory pub/sub with prioritiesOO designDesign and code a publish/subscribe system that runs on one machine: topics, subscribing, unsubscribing and publishing. Follow-up: messages carry a priority and higher-priority…Last asked Apr 2026
Implement team-style business logic with OOP, then roll out an API changeCodingThe interviewer describes logic similar to what the team builds and asks you to implement it with clean object-oriented design: classes, responsibilities and extension points…Last asked Apr 2026
Per-user token bucket limiter with interval refillsCodingBuild a per-user token rate limiter for an AI API. Every user has their own policy, and one user's traffic never affects another's. A policy has three positive integers: -…Last asked Apr 2026- Restaurant waitlist managerCodingBuild a waitlist for a restaurant: parties join with their size, may leave before being seated, and when a table frees up you seat the party that should get it. Keep each…Last asked Mar 2026
- Deck of cards with shuffle, draw and sortOO designModel a deck of playing cards with classes for cards and the deck. Implement a fair shuffle (every order equally likely, Fisher-Yates), drawing cards, and putting the deck back in…Last asked Mar 2026
- Editable sequence with a markerCodingDesign a sequence of elements with a marker on one of them. Support adding or removing a run of elements at a position, moving a run from one position to another, and setting a…Last asked Feb 2026
- Assign dorm rooms by student preferenceOO designYou get student IDs and room IDs. Each student prefers a two-person room or a four-person room. Design a system that assigns students to rooms according to their preferences. The…Last asked Feb 2026
- Backend for a game of checkersCodingBuild the backend of a checkers game under time pressure: board state, legal moves, captures and the win condition, with a data model you can explain. A working core matters more…Last asked Feb 2026
- Extensible employee cost calculatorOO designDesign the classes for a calculator that works out what employees cost the company. Different kinds of employees are costed differently, and new kinds or cost components will be…Last asked Feb 2026
Cart and pricing engine for a food delivery orderOO designIn a food delivery marketplace, an order's final price is more than the sum of its menu items: item customizations such as extra toppings and sizes change it, and so do other…Last asked Jan 2026- Design a poker gameOO designDesign the classes for a poker game: cards, deck, players, hands, betting rounds, and deciding the winner. Show the main methods, how a round flows from deal to showdown, and how…Last asked Jan 2026
- Design Amazon Locker (object-oriented)OO designModel a locker location with compartments of several sizes: assign a package to a compartment that fits, issue a pickup code, and handle expiry and returns.Last asked Jan 2026
- Design Amazon Kindle (object-oriented)OO designModel an e-reader library: buy and download books, keep several formats, track reading position across devices, and support highlights.Last asked Jan 2026
Simple VM manager with add, list, modify and deleteCodingWrite a simple manager for virtual machines: add a VM with its attributes, list VMs, modify a VM's attributes and delete a VM. Handle errors such as adding a duplicate id or…Last asked Nov 2025- Design a basic credit card systemOO designDesign the classes for a simple credit card system: cards and accounts, a credit limit, purchases, payments and the balance. Show how a purchase is authorized against the limit…Last asked Oct 2025
- Thread-safe single-machine chat server with channelsCodingBuild an in-process chat system where many clients join channels and post messages that the other members receive. Make it correct under concurrent senders and receivers, and…Last asked Oct 2025
- +1Design tic-tac-toeOO designModel an N-by-N tic-tac-toe game for two players: moves, turn order, and detecting a win or draw efficiently after each move.Last asked Oct 2025
Design a wallet with holds and payoutsOO designDesign and code a wallet for a rental platform. Users keep a balance; money can be put on hold (for example when a booking is made), then captured or released, and hosts receive…Last asked Sep 2025- Memory usage switcher with configurable thresholdsOO designDesign and code an in-memory switcher that watches memory usage and switches between states (or targets) when usage crosses thresholds the caller can configure. Cover how…Last asked Sep 2025
Shopping cart pricing with category couponsCodingA shopping cart holds items, each with a category and a price. A coupon names a category and gives a percentage or amount off, and it applies only when the cart meets its…Last asked Sep 2025- Refactor a rock-paper-scissors simulationCodingYou get existing code in which three bots play rock-paper-scissors against each other and the program prints how many games each bot won. Change it so the number of rounds is…Last asked Sep 2025
- Keyboard and mouse input systemOO designDesign classes for an input system that records what a user does with the keyboard and the mouse (key presses, clicks, movement) so that the program can tell what was input…Last asked Sep 2025
- Filter and analyze logs with an object-oriented designOO designDesign classes that read a stream of log entries, some of them errors, filter them by rules such as level, time range or source, and report simple analytics such as error counts…Last asked Sep 2025
- Configuration store with subscriber notificationsOO designDesign classes that let a system set configuration values while applications subscribe to the settings they care about. When a value changes, every subscriber of that setting is…Last asked Sep 2025
- Extensible event ticketing systemOO designWrite an EventTicketSystem that sells tickets for different kinds of events, such as concerts, movies and sports games. Adding a new kind of event later should not require…Last asked Sep 2025
- Price rides with fairness and poolingSystem designWrite and design the pricing logic of a ride-hailing service: compute a fare from distance, time and demand, keep prices fair between riders, and price pooled rides where several…Last asked Sep 2025
- Design a traffic light control systemOO designModel an intersection's traffic lights with phases and timings, pedestrian requests and an emergency override, as a clear state machine.Last asked Sep 2025
- Design a restaurant reservation serviceOO designModel restaurants, tables, time slots and reservations: search availability, book, modify and cancel, and avoid double-booking a table.Last asked Sep 2025
- Design Unix file searchOO designModel a find-like file search over a directory tree with composable filters (name pattern, size, type, extension) that are easy to extend.Last asked Aug 2025
- Delayed job schedulerOO designDesign and code a scheduler that accepts a job and a delay and runs the job after that many seconds. Cover the data structure that finds the next due job, the worker thread or…Last asked Aug 2025
- Thread-safe document and tag classesOO designDesign classes that record documents and the tags on them: add and remove tags, list a document's tags, and find documents by tag. Follow-up: many threads use it at once; make it…Last asked Aug 2025
Connect Four board with gravity drops and board snapshotsCodingBuild the board for a gravity-based four-in-a-row game. Players drop single-character colored pieces into columns. A piece falls straight down and stops in the lowest empty cell…- Two-player card game simulationCodingYou are building the engine for a simple two-player card game. Players are named "A" and "B". The deck is a list of distinct integers, and a higher integer beats a lower one…
- In-memory note-taking system with keyword searchCodingDesign an in-memory note-taking system, SecondBrainSystem. Each note gets a unique id and carries metadata about when it was created and last modified. Callers pass the current…
- Design an ATMOO designModel an ATM: card and PIN authentication, balance inquiry, withdrawal with a cash dispenser of fixed denominations, deposit, and failure handling.
- Design a vending machineOO designModel a vending machine with products, slots, coins and notes: select, pay, give change and handle sold-out items, using clear states.
- Design a food delivery system (object-oriented)OO designModel restaurants, menus, orders, couriers and order states for a food delivery app, including assignment and cancellation.
- Design a coffee makerOO designModel a coffee machine with recipes, ingredient containers and brewing steps; refuse drinks when ingredients run low and make adding recipes easy.
- Design a blackjack gameOO designModel a blackjack table with a dealer, players, a shoe of decks, bets, hit/stand/double/split, and payouts.