Master Topic View

3Sum

LC #15 · Two Pointers

4Sumext

LC #18 · Two Pointers

Abstract Factory

Provides an interface for creating families of related objects without specifying their concrete classes.

Adapter

Converts the interface of a class into another interface clients expect, enabling incompatible interfaces to work together.

Add and Search Words

LC #211 · Tries

Add Stringsext

LC #415 · Strings

Add Two Numbers

LC #2 · Linked List

Alien Dictionaryext

LC #269 · Graphs

All Oone Data Structureext

LC #432 · Design

Backspace String Compare

LC #844 · Stack

Baseball Game

LC #682 · Stack

Basic Calculatorext

LC #224 · Stack

Basic Calculator IIext

LC #227 · Stack

Best Time to Buy and Sell Stock

LC #121 · Sliding Window

Binary Search

LC #704 · Binary Search

Binary Search Tree Iteratorext

LC #173 · Trees

Binary Tree Level Order Traversal

LC #102 · Trees

Binary Tree Maximum Path Sum

LC #124 · Trees

Binary Tree Right Side Viewext

LC #199 · Trees

Binary Tree Vertical Order Traversalext

LC #314 · Trees

Bridge

Decouples an abstraction from its implementation so both can vary independently.

Builder

Separates the construction of a complex object from its representation using a step-by-step builder API.

Burst Balloons

LC #312 · Dynamic Programming

Car Fleet

LC #853 · Stack

Chain of Responsibility

Passes a request along a chain of handlers, each deciding to process it or pass it to the next handler.

Cheapest Flights Within K Stopsext

LC #787 · Graphs

Climbing Stairs

LC #70 · Dynamic Programming

Clone Graph

LC #133 · Graphs

Closest Binary Search Tree Valueext

LC #270 · Trees

Coin Change

LC #322 · Dynamic Programming

Combination Sum

LC #39 · Backtracking

Command

Encapsulates a request as an object, enabling parameterization, queuing, logging, and undo/redo operations.

Composite

Composes objects into tree structures to represent part-whole hierarchies, treating individual objects and compositions uniformly.

Construct Binary Tree from Preorder and Inorder Traversal

LC #105 · Trees

Container With Most Water

LC #11 · Two Pointers

Contains Duplicate

LC #217 · Arrays & Hashing

Contiguous Arrayext

LC #525 · Arrays & Hashing

Copy List with Random Pointerext

LC #138 · Linked List

Counting Bits

LC #338 · Math & Bit Manipulation

Course Schedule

LC #207 · Graphs

Course Schedule II

LC #210 · Graphs

CUDA Shared Memory & Memory Coalescing

GPU performance is bound by memory bandwidth. Shared memory + coalesced global access are the two highest-leverage CUDA optimizations. Required depth at NVIDIA and Tesla Autopilot.

Daily Temperatures

LC #739 · Stack

Decode Stringext

LC #394 · Stack

Decode Ways

LC #91 · Dynamic Programming

Decorator

Attaches additional responsibilities to an object dynamically by wrapping it in decorator objects.

Delete Operation for Two Stringsext

LC #583 · Dynamic Programming

Design a Distributed Cache (Memcached / mcrouter)

Consistent hashing, mcrouter routing, gutter pool, lease tokens. Meta E6+ infra design signature.

Design a Distributed Counter (Sharded + Eventually Consistent)

Sharded counters, eventual consistency, write-heavy. View counts, like counters, page views.

Design a Distributed File System (GFS / Colossus)

Master + chunkservers, replication, append-only writes, fault recovery. Foundation of modern data infra.

Design a Distributed Key-Value Store (DynamoDB-style)

Amazon's signature L5+ system design. Tests consistent hashing, replication, quorum, vector clocks, and the CAP trade-offs Amazon engineers grade for keenly. Based on the 2007 Dynamo paper.

Design a Distributed Rate Limiter

Token bucket, sliding window, Redis-backed. Asked at Meta E5+, Amazon, Stripe, Cloudflare.

Design a Global OTA Update System (Tesla Fleet)

Delta updates, staged rollout, canary, rollback, fail-safe, low-bandwidth, fleet segmentation.

Design a GPU Cluster Scheduler (MIG + Gang)

Bin packing, MIG slicing, gang scheduling, K8s GPU operator, preemption, QoS. NVIDIA signature SDI.

Design a URL Shortener (TinyURL / bit.ly)

Classic system-design starter. Tests capacity estimation, ID generation, read-heavy storage, caching, and analytics. Asked at Amazon, Microsoft, Uber, LinkedIn.

Design Amazon Customer-Order-Product DB

Relational + NoSQL hybrid, OLTP vs OLAP separation, global tables. Tests data-modeling decisions at multi-region scale.

Design Amazon Locker (IoT pickup network)

IoT device fleet, offline resilience, locker assignment, scanning, security/audit. Tests edge architecture + correctness under intermittent connectivity.

Design Amazon Order Processing (Saga + Idempotency)

Saga pattern across cart → payment → inventory → fulfillment. Tests distributed-transaction handling without 2PC.

Design Amazon Prime Video (Streaming + DRM)

Encoding pipeline, CDN, adaptive bitrate, viewing-state durability. Same primitives as Netflix Open Connect plus stricter DRM (PlayReady/Widevine/FairPlay).

Design Amazon Recommendation System

Candidate generation → ranking → re-ranking pipeline. Feature stores, A/B testing, real-time inference. Amazon signature SDI.

Design an Amazon Fulfillment Center System

Inventory tracking, robotics control, picking/packing optimization, order routing. Tests cyber-physical workflow design + real-time coordination at warehouse scale.

Design an E-Commerce Platform (Amazon-style)

Catalog + search + cart + order + payment + inventory + fulfillment decomposed into services. The "draw the whole company" architecture round.

Design an IDE (Visual Studio / VS Code)

Project model, language services, autocomplete, debugger plumbing. Microsoft-specific architecture round.

Design Apple Music (Streaming + Recommendations)

Catalog, recommendations, offline playback, CDN, royalties. Music streaming at scale.

Design Apple Push Notification Service (APNs)

Token management, fan-out, delivery, priority. Foundation of iOS notifications.

Design Azure VM Scheduler (Bin Packing + Fault Domains)

VM allocation, bin packing, fault domains, SLA-aware. Microsoft signature systems SDI.

Design Circular Queueext

LC #622 · Design

Design Distributed Training for 10B+ Param Model on 128 H100/B200

Tensor + pipeline + data parallelism, NCCL all-reduce, FP8/BF16, ZeRO/FSDP, checkpointing. NVIDIA signature SDI.

Design Dynamic Home-Screen Recommendations

Per-profile row construction, ranking, freshness, real-time signal incorporation. 2025 Netflix-reported prompt.

Design Facebook Live (Low-Latency Streaming + Live Comments)

Live video at scale + concurrent comments. Tests RTMP ingest + HLS/LL-HLS distribution + WebSocket fan-out.

Design Fault-Tolerant Distributed Training Pipeline

Checkpointing cadence, replica resurrection, NCCL recovery, elastic training. Survival in long-running jobs.

Design File Systemext

LC #1166 · Design

Design Find My / AirTag (Crowdsourced BLE Network)

BLE crowdsourced location, on-device crypto, anti-stalking, lost mode, battery-aware. Apple-specific signature SDI.

Design Fleet Management for Autonomous Vehicles (Robotaxi)

Real-time tracking, maintenance scheduling, route optimization, dispatch. Robotaxi vision system.

Design Gmail (Billions-Scale Email)

Email storage, search/indexing, spam filtering, threading. Tests inverted indexes + storage tiering.

Design Google Drive / Dropbox

File chunking, dedup, sync, version history, sharing/permissions. Classic SDI asked at all Mag7.

Design Google Maps (Tiles + Routing)

Geospatial DB, map tile serving, routing with Dijkstra/A*, real-time traffic, Street View tile pyramid.

Design Google Search Autocomplete (Type-Ahead)

Trie at scale, top-K ranking per prefix, freshness, multi-language. Most-asked Google + Amazon SDI.

Design Google's Web Crawler

URL frontier, politeness/rate limiting, dedup via hashing, distributed crawling, robots.txt. Signature Google SDI.

Design HashMapext

LC #706 · Design

Design Hit Counterext

LC #362 · Design

Design iCloud Photo Library Sync

Cross-device sync, conflict resolution, on-device + cloud, privacy-preserving. Apple signature SDI.

Design iMessage, End-to-End Encryption + Delivery

Apple ICT3+ canonical system design. Tests asymmetric crypto, multi-device key fan-out, offline delivery, and the privacy-first architecture Apple grades senior candidates on.

Design In-Memory File Systemext

LC #588 · Design

Design Instagram (Photo Upload + Feed + Stories)

Photo upload + feed + stories + search/explore + hashtags. E5+ Meta product-design canon.

Design Instagram Stories (24h TTL Ephemeral Feed)

24-hour TTL, view tracking, friend recency ordering. Ephemeral state at billions scale.

Design Kafka (Distributed Message Queue)

Partitioning, ISR, leader election, consumer groups. Meta E6+ infra signature.

Design LLM Inference Serving (Triton + vLLM + PagedAttention)

Triton Inference Server, dynamic batching, KV-cache management, tensor parallelism, paged attention.

Design Messenger / WhatsApp (E2E + Group Chat)

End-to-end encryption (Signal protocol), message delivery guarantees, group chat, read receipts, multi-device. Meta signature SDI.

Design Meta News Feed, Fan-out at Scale

Meta's E5+ Product Design canon. Push (fan-out-on-write) vs Pull (fan-out-on-read) vs hybrid. The interviewer wants the trade-off math, not a buzzword tour.

Design Microsoft Teams (Chat + Presence + Voice/Video)

Channels + persistent chat + presence + voice/video + meetings. Microsoft's most-asked SDI.

Design Netflix Encoding / Transcoding Pipeline

Per-title encoding, per-shot encoding, AV1, codec ladder, GPU-accelerated encoding, cost optimization.

Design Netflix Open Connect (Streaming CDN)

Netflix's purpose-built CDN serving 200M+ users. Tests bitrate adaptation, edge placement, manifest design, and capacity planning. Open-ended senior-loop favorite.

Design Netflix Recommendation Engine

Offline candidate generation + online ranking, "row-of-rows" homepage, A/B testing infra, personalization signals.

Design Netflix Video Streaming End-to-End

Encoding pipeline → multi-bitrate manifest → Open Connect CDN → ABR playback → resume, sub-2s start, 99.99% availability.

Design OneDrive (File Sync Across Devices)

File sync, version history, large-file upload, deltas. Microsoft signature SDI.

Design Outlook / Exchange (Enterprise Mail Server)

Storage, search, calendar integration, anti-spam. Enterprise mail + calendar + tasks combined.

Design Real-Time Autonomous-Vehicle Data Ingestion Pipeline

Vehicle → edge → cloud, sensor data compression, Kafka/Pulsar, hot/cold tiering, retraining loop.

Design Redis (Single-Threaded + Persistence + Cluster)

Single-threaded event loop, RDB+AOF persistence, replication, cluster mode. Meta E6+ infra round.

Design Search Autocomplete Systemext

LC #642 · Tries

Design Supercharger Network Management

Real-time station availability, load balancing of grid power, reservations, in-car nav integration, dynamic pricing.

Design Teams Voice & Video (WebRTC + Signaling)

WebRTC, signaling, TURN/STUN, recording. Real-time low-latency media.

Design Tesla Autopilot Data Pipeline (Auto-labeling + Retraining)

Auto-labeling, shadow mode, rare-event mining, training data curation, reprocessing.

Design Tesla Fleet Telemetry Pipeline

Vehicle → edge → cloud, millions of vehicles, sensor data compression, hot/cold tiering, anomaly detection. Tesla #1 SDI.

Design the App Store (Catalog + Distribution)

Catalog, search, payments, review system, distribution at scale, regional availability.

Design Twitter

LC #355 · Heap

Design YouTube (Video Upload + Encoding + CDN)

Prototypical Google SDI. Video upload, encoding pipeline, CDN, view counts, recommendations, comments.

Design YouTube Watch History

Google L4+ favorite. Tests append-only event ingestion, time-partitioned storage, materialized views for "Continue Watching," and read-time aggregations under privacy constraints.

Diameter of Binary Treeext

LC #543 · Trees

Edit Distance

LC #72 · Dynamic Programming

Employee Free Timeext

LC #759 · Intervals

Evaluate Reverse Polish Notation

LC #150 · Stack

Facade

Provides a simplified interface to a complex subsystem, hiding its internal complexity from clients.

Factory Method

Defines an interface for creating an object but lets subclasses decide which class to instantiate.

Find Leaves of Binary Treeext

LC #366 · Trees

Find Median from Data Stream

LC #295 · Heap

Find Minimum in Rotated Sorted Array

LC #153 · Binary Search

Find Peak Element

LC #162 · Binary Search

Find Pivot Indexext

LC #724 · Strings

Find the Index of the First Occurrence (strStr)ext

LC #28 · Strings

Find the Town Judge

LC #997 · Graphs

First Missing Positiveext

LC #41 · Strings

Flyweight

Uses sharing to support large numbers of fine-grained objects efficiently by separating intrinsic and extrinsic state.

Gas Stationext

LC #134 · Greedy

Generate Parenthesesext

LC #22 · Math & Bit Manipulation

Group Anagrams

LC #49 · Arrays & Hashing

House Robber

LC #198 · Dynamic Programming

House Robber II

LC #213 · Dynamic Programming

Implement Trie

LC #208 · Tries

Insert Delete GetRandom O(1)ext

LC #380 · Design

Insert Interval

LC #57 · Intervals

Integer to English Wordsext

LC #273 · Strings

Interleaving Stringext

LC #97 · Dynamic Programming

Interpreter

Defines a grammar for a language and provides an interpreter to evaluate sentences in that language.

Intersection of Two Arrays

LC #349 · Arrays & Hashing

Invert Binary Tree

LC #226 · Trees

Iterator

Provides a way to sequentially access elements of a collection without exposing its underlying structure.

Jump Game

LC #55 · Dynamic Programming

K Closest Points to Originext

LC #973 · Heap

Kids With the Greatest Number of Candiesext

LC #1431 · Arrays & Hashing

Koko Eating Bananas

LC #875 · Binary Search

Kth Largest Element in an Array

LC #215 · Heap

Kth Smallest Element in BST

LC #230 · Trees

Largest Rectangle in Histogram

LC #84 · Stack

Last Stone Weight

LC #1046 · Heap

Least Number of Unique Integers after K Removalsext

LC #1481 · Arrays & Hashing

LFU Cacheext

LC #460 · Design

Linked List Cycle

LC #141 · Linked List

Linked List Cycle IIext

LC #142 · Linked List

Logger Rate Limiterext

LC #359 · Design

Longest Common Prefixext

LC #14 · Strings

Longest Consecutive Sequence

LC #128 · Arrays & Hashing

Longest Increasing Subsequence

LC #300 · Dynamic Programming

Longest Palindromic Substring

LC #5 · Dynamic Programming

Longest Repeating Character Replacement

LC #424 · Sliding Window

Longest Substring Without Repeating Characters

LC #3 · Sliding Window

Longest Valid Parenthesesext

LC #32 · Dynamic Programming

Lowest Common Ancestor

LC #236 · Trees

Lowest Common Ancestor of a BT IIext

LC #1644 · Trees

Lowest Common Ancestor of a BT IIIext

LC #1650 · Trees

Lowest Common Ancestor of BST

LC #235 · Trees

LRU Cache

LC #146 · Linked List

LRU Cache, Hash Map + Doubly Linked List

O(1) get/put cache with bounded capacity by combining a hash map (key → node) with a doubly linked list (recency). One of the most-asked LC mediums across Mag7.

Majority Element

LC #169 · Arrays & Hashing

Max Area of Island

LC #695 · Graphs

Max Consecutive Ones IIIext

LC #1004 · Arrays & Hashing

Maximum Average Subarray I

LC #643 · Sliding Window

Maximum Depth of Binary Tree

LC #104 · Trees

Maximum Number of Balloonsext

LC #1189 · Strings

Maximum Product Subarray

LC #152 · Dynamic Programming

Maximum Profit in Job Schedulingext

LC #1235 · Intervals

Maximum Subarrayext

LC #53 · Strings

Median of Two Sorted Arrays

LC #4 · Binary Search

Mediator

Defines an object that encapsulates how a set of objects interact, reducing direct dependencies between them.

Meeting Rooms

LC #252 · Intervals

Meeting Rooms II

LC #253 · Intervals

Memento

Captures and externalizes an object's internal state without violating encapsulation, enabling later restoration.

Merge Intervals

LC #56 · Intervals

Merge K Sorted Lists

LC #23 · Linked List

Merge Sorted Array

LC #88 · Two Pointers

Merge Two Sorted Lists

LC #21 · Linked List

Middle of the Linked List

LC #876 · Linked List

Min Stack

LC #155 · Stack

Minimum Area Rectangleext

LC #939 · Math & Bit Manipulation

Minimum Interval to Include Each Queryext

LC #1851 · Greedy

Minimum Path Sumext

LC #64 · Dynamic Programming

Minimum Size Subarray Sum

LC #209 · Sliding Window

Minimum Window Substring

LC #76 · Sliding Window

Missing Number

LC #268 · Math & Bit Manipulation

Move Zeroesext

LC #283 · Strings

My Calendar Iext

LC #729 · Intervals

N-Queens

LC #51 · Backtracking

Network Delay Timeext

LC #743 · Graphs

Non-overlapping Intervals

LC #435 · Intervals

Null Object

Provides a default object with do-nothing behavior instead of null, eliminating null checks throughout code.

Number of 1 Bits

LC #191 · Math & Bit Manipulation

Number of Connected Components in an Undirected Graph

LC #323 · Graphs

Number of Islands

LC #200 · Graphs

Object Pool

Maintains a pool of reusable objects to avoid the cost of creating and destroying them on demand.

Observer

Defines a one-to-many dependency so when one object changes state, all its dependents are notified automatically.

One Edit Distanceext

LC #161 · Strings

Pacific Atlantic Water Flow

LC #417 · Graphs

Palindrome Partitioning

LC #131 · Backtracking

Palindromic Substrings

LC #647 · Dynamic Programming

Partition Equal Subset Sum

LC #416 · Dynamic Programming

Partition Labelsext

LC #763 · Greedy

Permutation in String

LC #567 · Sliding Window

Permutations

LC #46 · Backtracking

Populating Next Right Pointers IIext

LC #117 · Trees

Populating Next Right Pointers in Each Nodeext

LC #116 · Trees

Pow(x, n)ext

LC #50 · Math & Bit Manipulation

Power of Twoext

LC #231 · Math & Bit Manipulation

Product of Array Except Self

LC #238 · Arrays & Hashing

Prototype

Creates new objects by cloning an existing instance, avoiding expensive re-initialization.

Proxy

Provides a surrogate or placeholder for another object to control access to it.

Random Pick with Weightext

LC #528 · Math & Bit Manipulation

Reconstruct Itineraryext

LC #332 · Graphs

Rectangle Areaext

LC #223 · Math & Bit Manipulation

Redundant Connection

LC #684 · Graphs

Regular Expression Matchingext

LC #10 · Dynamic Programming

Remove Duplicates from Sorted Array

LC #26 · Two Pointers

Remove Nth Node From End

LC #19 · Linked List

Reorder List

LC #143 · Linked List

Reorganize Stringext

LC #767 · Strings

Reverse Bits

LC #190 · Math & Bit Manipulation

Reverse Linked List

LC #206 · Linked List

Reverse Linked List IIext

LC #92 · Linked List

Reverse Nodes in k-Groupext

LC #25 · Linked List

Reverse Words in a Stringext

LC #151 · Strings

Robot Room Cleanerext

LC #489 · Graphs

Rotate Imageext

LC #48 · Math & Bit Manipulation

Rotting Orangesext

LC #994 · Graphs

Same Tree

LC #100 · Trees

Score of Parenthesesext

LC #856 · Stack

Search in Rotated Sorted Array

LC #33 · Binary Search

Search Insert Position

LC #35 · Binary Search

Serialize and Deserialize Binary Tree

LC #297 · Trees

Set Matrix Zeroesext

LC #73 · Math & Bit Manipulation

Shortest Distance from All Buildingsext

LC #317 · Graphs

Shortest Path in Binary Matrixext

LC #1091 · Graphs

Simplify Pathext

LC #71 · Stack

Single Number

LC #136 · Math & Bit Manipulation

Single-Threaded CPUext

LC #1834 · Heap

Singleton

Ensures a class has only one instance and provides a global access point to it.

Sort Colors

LC #75 · Two Pointers

Spiral Matrixext

LC #54 · Math & Bit Manipulation

Sqrt(x)

LC #69 · Binary Search

STAR & STAR-L Method for Behavioral Stories

Structured story format used by every Mag7 behavioral round. Google extends to STAR-L (Learnings). Amazon expects 1 LP per story. Netflix tunes to culture pillars.

State

Allows an object to alter its behavior when its internal state changes, appearing to change its class.

Strategy

Defines a family of algorithms, encapsulates each one, and makes them interchangeable at runtime.

String to Integer (atoi)ext

LC #8 · Strings

Subarray Sum Equals Kext

LC #560 · Arrays & Hashing

Subsets

LC #78 · Backtracking

Subtree of Another Tree

LC #572 · Trees

Sum of Two Integers

LC #371 · Math & Bit Manipulation

Surrounded Regionsext

LC #130 · Graphs

Swim in Rising Waterext