+7Design a distributed web crawlerSystem designCrawl billions of web pages politely and repeatedly, deduplicating URLs and content, to feed a search index or a training-data pipeline.
Last asked Oct 2026
#queues
- +7
- Work queue with a dead-letter queue and dependency cycle detectionCodingBuild an in-memory work queue for pipeline tasks that depend on each other (download, then tokenize, then train). Workers call nextready() to take a task and report back with…Last asked Oct 2026
- Fault-tolerant work queue with leases and retriesCodingImplement an in-memory work queue that keeps working when workers crash. Workers take a task, process it, and report success or failure. A worker that dies silently must not lose…Last asked Oct 2026
Document indexing queue assignmentCodingAssign incoming documents to indexing workers across queues so the load stays balanced as documents arrive. Reported on 1point3acres' Glean bank; reconstructed in our own words.Last asked Sep 2026- +1Design a video generation service on a scarce GPU poolAI system designUsers 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 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
+4Design a notification systemSystem designA shared service other teams call to send push, email and SMS notifications: templates, user preferences, retries, deduplication and rate limits.Last asked Sep 2026
Design a matchmaking service for an online gameSystem designDesign a matchmaking service. It must let players join the queue and cancel, match two compatible players, notify both when a match is found, and deal with disconnects and…Last asked Sep 2026- Inference loop with continuous batching over a mock modelCodingYou get a model function that takes a batch of sequences and returns one next token for each. Write the serving loop: keep a fixed number of batch slots full, retire a sequence…Last asked Sep 2026
+12Design a distributed job schedulerSystem designDesign a service that runs millions of scheduled and on-demand jobs (cron-like and one-off) reliably across a fleet of workers.Last asked Sep 2026
Linked-list queue with deletionsCodingImplement a queue on a linked list with enqueue and dequeue, then extend it through follow-ups that delete elements from the queue.Last asked Sep 2026
Schedule video processing across CPU and GPU workersSystem designVideo processing jobs have stages, some suited to CPUs and some to GPUs. Design how jobs are split into stages and scheduled across the two pools of machines to keep both busy…Last asked Aug 2026
Hit counter for the last five minutesCodingRecord hits (or events) as they arrive with a timestamp, and answer how many happened in the last five minutes (more generally, the last W seconds) at any moment. Discuss which…Last asked Aug 2026
+3Fixed-capacity circular bufferCodingImplement a generic FIFO buffer with a fixed capacity, allocated once up front, with constant-time push and pop. Discuss how to signal full and empty and how the buffer would be…Last asked Aug 2026- Order service whose database write succeeds but queue publish failsSystem designDesign the order path of an online bookstore. When an order request arrives, the service inserts the order into its database and then publishes a message to a queue (Amazon SQS)…Last asked Aug 2026
Fill an order from the oldest inventory batches firstCodingA warehouse keeps stock in batches received at different times. Fill an order by taking units from the oldest batches first, moving to newer batches as each one runs out. Return…Last asked Aug 2026
+4Design a ticket booking systemSystem designSell seats for concerts and games where demand spikes the moment sales open: hold seats briefly, never sell one twice, and stay up under the rush.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
- Queue using two stacksCodingImplement a first-in, first-out queue (push, pop, peek, empty) using only two stacks. Move items from the input stack to the output stack only when the output stack is empty, and…Last asked Jun 2026
- Design a customer support ticketing systemSystem designCustomers open tickets by email, chat or web; agents get them routed by skill and priority, with SLAs, escalation and full history.Last asked Jun 2026
- Filter events and route them to queuesCodingProcess a stream of events: apply filter rules to each one and route every event that passes to the right queue.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
- +3Design LeetCodeSystem designUsers solve coding problems in the browser; run their submissions safely against hidden tests, return verdicts quickly, and support live contests with leaderboards.Last asked May 2026
Design a PDF-to-Markdown inference API (sync and async)AI system designBuild a service that turns PDF files into Markdown out of three existing functions: one that splits a PDF into page images (CPU-heavy), an OCR model that reads a page image or a…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
Design a driver queue for a pickup areaSystem designDrivers waiting in a dedicated pickup area join a queue and are offered trips in order. Design it: how drivers enter and leave the queue, how their place is kept fairly, and how…Last asked Feb 2026- Design a content moderation systemSystem designScreen user posts, images and videos for policy violations with ML classifiers and human reviewers, acting within seconds on the worst content.Last asked Feb 2026
Thread-safe task queue on a linked listCodingA task queue was written for one thread: a singly linked list with head and tail, where put appends at the tail and get removes from the head. Explain what goes wrong when many…Last asked Feb 2026- Hit counter over a sliding time windowCodingBuild a counter that records events with timestamps and reports how many happened in the last five minutes. Timestamps arrive in non-decreasing order. Reported variants: counts…Last asked Jan 2026
- Moving average from a data streamCodingImplement a class that receives numbers one at a time and returns the average of the last size values after each one, in constant time per call, keeping a running sum and a queue…Last asked Jan 2026
Alert trigger and resolve events from merchant error logsCodingYou get transaction logs with timestamp, merchantid, statuscode and count. For each (merchantid, statuscode) pair, emit a TRIGGER event when that error's count over a recent time…Last asked Jan 2026- Design CRUD APIs backed by asynchronous jobsSystem designDesign a service that exposes create, read, update and delete APIs for a resource, where some operations start long-running work that cannot finish inside the request. Cover the…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
- Design Airbnb's notification systemSystem designSend booking confirmations, reminders and host messages over push, email and SMS, respecting user preferences and time zones, without duplicates.Last asked Dec 2025
- +1Design a webhook delivery systemSystem designDeliver event notifications to customers' HTTP endpoints at least once, with retries and backoff, signing, ordering where it matters, and isolation from slow endpoints.Last asked Dec 2025
- +2Design 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.Last asked Sep 2025
- Design a job schedulerSystem designDesign a service that runs jobs for other teams: jobs can run once, at a given time or on a recurring schedule. Cover how jobs are submitted and stored, how the scheduler finds…Last asked Sep 2025
- Inventory allocation with backordersCodingOrders arrive for products whose stock is limited. Allocate stock to orders as they come in; when a product runs out, record the unfilled part as a backorder and fill backorders…Last asked Jul 2025
- Design a waitlist for in-demand listingsSystem designWhen a popular listing is not available for the dates a guest wants, the guest can join a waitlist. Design the API and system behind it: joining and leaving, detecting when the…Last asked Jul 2025