Key-value cache with per-entry TTLCodingImplement an in-memory key-value cache where every write gives a key, a value and a time-to-live. Once an entry's time is up it must behave as if it was never written. Support…
Last asked Oct 2026
#caching
+5Implement an LRU cacheCodingImplement a least-recently-used cache with get(key) and put(key, value), both in O(1) time, with a fixed capacity.Last asked Oct 2026
+1Design a feature flag serviceSystem designLet teams turn features on for a percentage of users or specific accounts, with changes reaching every service within seconds and no per-request network call.Last asked Oct 2026
+8Design typeahead suggestionsSystem designSuggest completions as the user types into a search box, within tens of milliseconds, ranked by popularity and fresh with trending queries.Last asked Sep 2026
Design the data flow behind a food delivery restaurant listSystem designWhen a customer opens a food delivery app with a delivery address, the home screen lists the restaurants that can deliver there. Design how restaurant data travels from the…Last asked Sep 2026
Explore a friend graph through a remote API with few callsCodingYou cannot read a social graph directly; the only access is getfriends(userid), a remote call that returns a user's friends and costs a network round trip. Write code that…Last asked Sep 2026
Cut read latency in an existing relational database designSystem designYou are shown the database design behind a real service: a relational store that has become slow to read. Propose how you would change it to bring read latency down. Start by…Last asked Sep 2026
Fix a function-cache key function, then make it durableCodingA small memoizing cache for arbitrary callables has a broken key function that mishandles positional versus keyword arguments and defaults. Fix the keying first, then extend the…Last asked Sep 2026- Find the bugs in a dictionary memoization cache under concurrencyCodingA slow function is wrapped by a module-level dictionary that stores its results: look up the key, otherwise compute and store. You are shown the code and asked what breaks in…Last asked Sep 2026
- +7LRU cacheCodingBuild a key-value cache with a fixed capacity that evicts the least recently used entry when it is full. get(key) returns the value or a miss, put(key, value) inserts or updates…Last asked Sep 2026
Design a distribution-center inventory update serviceSystem designDistribution centers send stock updates. Design the service that keeps the latest quantity, availability and last-update time for every location and item pair and answers lookups…Last asked Sep 2026
Design a book price aggregatorSystem designShow the current price of a book across many online sellers, keeping prices fresh while respecting each seller's API limits.Last asked Sep 2026- Design a single-node in-memory cache with a write-ahead logSystem designDesign an in-memory key-value cache that sits inside one web service. Then make it survive restarts with a write-ahead log, and explain how you would shard it and cut lock…Last asked Sep 2026
Design a global caching service for small imagesSystem designDesign a global caching service for small images, backed by a single database that holds every image and is the source of truth. Cover the read path, the update path, the cache…Last asked Sep 2026- Design a distributed file system for large structured datasetsSystem designDesign a distributed file system or storage service for large structured datasets that data-processing jobs read and write. Go past the box diagram and walk through the concrete…Last asked Sep 2026
Design distributed storage for build artifactsSystem designDesign a storage system for build artifacts: binaries, packages and archives produced by the build pipeline that later stages download to test and deploy. Cover the upload and…Last asked Sep 2026
+3Design a nearby points-of-interest serviceSystem designGiven a user's location, return the closest restaurants, shops and other places of interest within a radius, fast, for a read-heavy global audience.Last asked Sep 2026- +6Design TinyURLSystem designTurn long URLs into short links and redirect visitors fast, at billions of redirects a day, with optional custom aliases and expiry.Last asked Sep 2026
+1Design an online game leaderboardSystem designShow the top players and each player's own rank in real time as millions of scores update.Last asked Sep 2026- Design a content delivery networkSystem designDesign a CDN that serves static content from servers close to users. Cover how a request reaches the nearest edge, what the edge caches and for how long, cache misses and the path…Last asked Sep 2026
Design a to-do list service: CRUD, auth, rate limits, caching, versioningSystem designDesign the backend for a to-do list app: create, read, update and delete tasks, user authentication, rate limiting, caching, and versioning the API as it changes. Only the title…Last asked Jun 2026- Design a low-latency product price update APISystem designDesign an API that updates the prices of specific products and makes the new prices visible quickly to everything that reads them. Cover the write path, how readers and caches…Last asked Apr 2026
- Deduplicate concurrent downloads of the same URLCodingWrite a downloader that many threads call with URLs. Downloads of different URLs run in parallel. When several threads ask for the same URL at the same time, only one of them…Last asked Apr 2026
- Autocomplete data fetching with debounce, retry and cachingCodingThe UI of an autocomplete box is already built; you write only the data-fetching logic behind it. Debounce requests while the user types, retry requests that fail, show only the…Last asked Apr 2026
- Design a read-heavy service for org chart subordinate countsSystem designGiven manager-report relationships for a company, answer "how many people are under this person?" for any employee, at high read volume. Then handle changes: when a reporting…Last asked Feb 2026
- Design a multi-provider financial dashboardSystem designDesign a dashboard that shows each user financial metrics such as account balances and stock holdings. The data comes from several external providers, such as stock data feeds…Last asked Feb 2026
- LFU cache, then distribute itCodingDesign and implement a least-frequently-used cache with get and put in O(1), evicting the least used key and, among ties, the least recently used. The input then becomes a stream…Last asked Nov 2025
- Serve happy number checks at scaleSystem designA service answers whether a number eventually reaches 1 when you keep replacing it with the sum of the squares of its digits. Scale it to a large volume of requests: caching or…Last asked Oct 2025
- Serve inventory from disk when it doesn't fit in memorySystem designDesign a service that answers inventory lookups from data that lives on disk because it is too large to keep in memory. Cover the on-disk layout and index, what you cache in…Last asked Oct 2025
- Design a flight search serviceSystem designDesign a service where users search flights by origin, destination and dates and see prices and availability. Cover where fare data comes from and how fresh it must be, caching…Last asked Oct 2025
Design a cache for query views that depend on each otherSystem designIn a data warehouse, views are defined on top of tables and other views, so the views form a DAG. Design a cache that speeds up queries over these views and keeps it correct when…Last asked Sep 2025- Design reliable sign-in on top of a flaky token providerSystem designClients get a token from a third-party auth server and present it to your main server. The third-party server is unreliable: requests fail sometimes, and sometimes it answers with…Last asked Sep 2025
Sum tree with node values computed from childrenCodingA tree's leaves hold numbers, and every other node's value is the sum of its children. Return the value of any node. Then support changes: turn a node into a leaf with a value, or…Last asked Sep 2025- Concurrent caching client for byte-range file readsSystem designDesign a client that reads byte ranges of remote files and caches what it has fetched, so a later read of a range it already holds is served locally. Many threads use one client…Last asked Aug 2025
LRU cache where each item counts by its quantityCodingImplement an LRU cache in which every item carries a quantity, and capacity is measured in total quantity rather than number of items. A put may evict several least recently used…Last asked Aug 2025- LFU cacheCodingImplement a least-frequently-used cache with get and put in O(1). When full, evict the key used least often, breaking ties by least recently used. Keep a map from key to node and…Last asked Jul 2025
Guided system design fundamentals roundSystem designAn interviewer-led system design exercise covering requirements, architecture, storage, caching, async work, reliability and observability for a supplied scenario. Reported on…
Read-through and write-through cache adapterCodingImplement a cache adapter that reads through to the backing store on misses and writes through on updates. Reported on 1point3acres' Harvey bank; reconstructed in our own words.