Get problems in a range. If start and end are not provided, get all problems with default page size.

{
  problems: [
    { id: string, title: string, difficulty: string }
  ]
}


Get problem details, including description, constraints, examples, and starter code.

{
  id: string
  title: string
  difficulty: string
  description: string
  constraints: string
  examples: [{
    input: string
    output: string
  }]
  starter_code: {
    language: string
    code: string
  }
}


Submit code for a problem and get results.

{
  user_id: string
  code: string
  language: string
}


{
  status: success | fail
  test_cases: [
    { status: success | fail | timeout }
  ]
}


{
  ranking: [
    { user_id: string, score: number }
  ]
}


API Server

Isolated execution in a virtualized environment

Virtual Machine (VM)

Lightweight, isolated execution environments

Container (Docker)

Event-driven, auto-scaling code execution

Serverless Function

Code Execution Options

In-memory data structure store, using ZSET for leaderboard

Redis Sorted Set

NoSQL Database

Custom implementation using heap or similar structure

In-Memory Data Structure

Specialized database for time-based data (e.g., InfluxDB)

Time-Series Database

Leaderboard Implementation Options

Design a coding contest platform like LeetCode.

Test Case Execution

Test Case Storage

Failure Handling

Resource Limitation

Isolation Techniques

Real-Time Leaderboard Updates

Limitation Strategies

Client

Problems Service

Database

View Problems

Code Evaluation Service

Message Queue

Code Execution Workers

Submit Solution

Contest Service

Leaderboard Storage

Coding Contest

Availability

Latency

Security

Storage

Design LeetCode Online Judge | System Design Interview Question

Design LeetCode

Shorten a given long URL and return the shortened URL.

{
  "shortUrl": "http://urlshort.ly/abcd"
}


Redirect to the original long URL using the shortened URL.

Design a URL Shortener service like bit.ly

Properties

Unique ID Generation

Encoding IDs

Sharding

Database Considerations

Pre-Generating IDs

Service

URL Shortening

API Gateway

Request Handler

Caching Layer

URL Redirection

Analytics Service

In-Memory Database

Link Analytics

Durability

Design URL Shortener | System Design Interview Question

Design URL Shortener

Receive webhooks from external systems, returns 200 OK if the event is accepted.

API Endpoint

Design a webhook service that processes incoming requests and ensures efficient, secure handling of real-time events, such as payment notifications from services like Stripe or Shopify.

If you prefer the video format, here's a walkthrough of the problem:
<iframe width="560" height="315" src="https://www.youtube.com/embed/4C9SVQVmUxs?si=VLTgs_oXCJf3TbI7" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>


Security Measures

Duplicate Request Handling

Out-of-Order Requests

Client Service

Accept API Calls to Receive Event Notifications

Improved Scalability

Monitoring and Alerting

High Availability and Resilience

At-least-once processing

Webhook System Design | System Design Interview Question

Design Webhook

{
  "documentId": "doc-123",
  "title": "My Document"
}


{
  "documentId": "doc-123",
  "title": "My Document",
  "content": "Document content"
}


{
  "title": "Updated Title",
  "content": "Updated content"
}


{
  "documentId": "doc-123",
  "title": "Updated Title"
}


WebSocket endpoint for real-time collaboration. After connection is established, 
messages are exchanged in both directions using the WebSocket protocol.

Example message from server:
{
  "type": "operation",
  "userId": "user-789",
  "operation": {
    "type": "insert",
    "position": 10,
    "text": "new text"
  }
}

Example message from client:
{
  "type": "operation",
  "operation": {
    "type": "insert",
    "position": 15,
    "text": "client text"
  }
}


Client periodically requests updates from server

HTTP Polling

WebSocket

Server pushes updates to client over HTTP

Server-Sent Events (SSE)

Synchronization Protocol Options

Design a collaborative editing system like Google Docs.


Versioning Strategies

Version Metadata

Storage Optimization

Access Control

Managing Server Load

CRDTs

Operational Transformation

Local Storage

Conflict Resolution Strategies

Sync Process

Object Storage

Single User Editing

Websocket

Conflict Resolution

Synchronization

Multi-user Collaborative Editing

Google Docs' Document Structure

Operational Transformation (Wikipedia)

Conflict-free Replicated Data Types (CRDTs)

Google Docs System Design | System Design Interview Question

Design a Collaborative Editing System like Google Docs

Return the top k most played songs in the last time window (1 day in this case). The time window is optional and defaults to all time if not specified. The response is a list of items with their IDs and play counts.

{
  items: [
    { id: string, count: number }
  ]
}


Round-robin partitioning distributes events evenly across partitions.

Round-Robin

Fixed Hash

[Consistent Hashing](/fundamentals/consistent-hashing) is used to dynamically adjust the number of partitions.


Dynamic Hash

Partitioning Schemes

Design a system to find the top k heavy hitters in a stream of data. This could be
- the top k most played songs in a music streaming service like Spotify
- the top k most viewed videos on a video streaming service like YouTube
- the top k most bought items in an e-commerce service like Amazon
- the top k most frequent items in a social media service like Twitter
- the top k most accessed IP addresses on a network


Approximation Techniques

Count-Min Sketch

Trade-offs

Data Structure

Algorithm to Maintain Top-K

Global Window Top K, Low QPS

Scaling Strategies

Global Window Top K, High QPS

Sliding Window Top K, High QPS

Accuracy

Design Spotify Top K Songs, Top K Heavy Hitters | System Design Interview Question

Design Spotify Top K Songs

Yelp is an online platform that publishes crowd-sourced reviews about businesses. It also trains small businesses to respond to reviews responsibly; hosts social events for reviewers; and provides data about businesses, including health inspection scores. Yelp.com is a popular platform for users to find and review new places to eat, shop, drink, relax, and play.


Design Yelp

A rate limiter is a system is to prevent a user from making too many requests to a service within a certain time frame. This is used to protect services from abuse and can be implemented in various scopes like per user, per IP address, etc.


Design Rate Limiter

Pastebin is an online application where users can store plain text. It is often used by developers to store pieces of sources code or configuration information, but anyone can essentially store any type of text. The idea behind the site is to make it more convenient for people to share large amounts of text online. Each piece of text that is pasted on Pastebin can be accessed through a unique URL


Design Pastebin

Design a realtime server monitoring and alert system like Datadog.

Design Realtime Monitoring System

A typeahead system, often called autocomplete, is a feature in software programs that predicts the rest of a word or phrase that a user is typing. This functionality helps users to find and select from a pre-populated list of values as they type, reducing the amount of typing needed and making the input process faster and more efficient.

An everyday example of a typeahead system is Google's search box. As you begin typing your search query, Google provides a dropdown list of suggested search terms that match what you have typed so far. These suggestions are based on popular searches and the content indexed by Google's search engine. This allows you to see and select your intended search without having to type out the entire term, making the search process faster and more efficient.

When a user begins to type in the search box, the typeahead feature could suggest book titles, authors, or genres that match the typed characters. For instance, if the user types in "Har", the system could suggest "Harry Potter", "Harper Lee", etc. This kind of typeahead system can greatly enhance the user experience by providing instant feedback and helping users formulate their search queries.

In this problem, we will design a typeahead system for a large e-commerce site. The system will provide search suggestions to users as they type in the search box. The suggestions will be based on the most popular searches and the content indexed by the e-commerce site's search engine.


Design Typeahead System

Design a comment system, such as Disqus, is a feature integrated into websites that allows users to post comments on published content, interact with other users through replies, upvote or downvote comments, and sort or filter comments. This system must be robust, scalable, and efficient to handle a large volume of users and comments.

Design a Comment System

Design a simplified version of Twitter where users can post tweets, follow/unfollow other users and is able to see the tweets of its followings.

Design Twitter

WhatsApp System Design: Building a Scalable Messaging App like WeChat, Telegram, and Messenger

Design WhatsApp

Design a file hosting service such as Dropbox or Google Drive.
A cloud file hosting service allows users to upload, download, and share files across different platforms.
It should support multiple file types including text, images, and multimedia formats.
For this problem let's focus on the backend system that stores and syncs them between different devices.


Design Dropbox

YouTube is an online video-sharing platform where users can upload, share, and view videos. It supports various types of videos, including TV show clips, music videos, short and documentary films, movie trailers, and other content such as video blogging (vlogging), short original videos, and educational videos.


Design YouTube

Uber System Design: Building a Scalable Ride-Hailing Service

Design Uber

Design a mapping service like Google Maps

Design Google Maps

Design a event ticketing system like TicketMaster

Design TicketMaster

Netflix is a streaming service offering a wide array of TV shows, movies, anime, documentaries, and more on thousands of internet-connected devices. Unlike YouTube, which primarily hosts user-generated content, Netflix focuses on delivering professionally produced film and television content, providing users with access to a vast library of titles without the need to watch a single commercial.


System Design Problems