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All practice problemsCoding, design and hands-on challenges.Repository CodingHands-onFix bugs and build in a real codebase.Code ReviewHands-onFind risks and explain your verdict.Data structures & algorithmsCore patterns to advanced algorithms.Machine learningImplement ML and numerical methods.SQL & databasesQueries, data and analytical problems.HLD system designScalable architecture and tradeoffs.LLD system designObjects, interfaces and behavior.Aptitude & previous-year papersAptitude topics and exam practice.AI interview prepRehearse interviews with an AI tutor.Online compilerWrite and run code in your browser.

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Learning pathsConnect lessons, visualizers and practical challenges.Algorithm visualizersStep through algorithms and see how they work.Books & readingBring your PDFs, take notes and study with AI.Daily current affairsUnderstand the news, save notes and revise the brief.Data structures & algorithmsLearn the foundations of efficient problem solving.Machine learningBuild mathematical intuition and explore ML concepts.SQL & databasesUnderstand data models, queries and transactions.System designStudy architecture, distributed systems and object design.
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101OneNoughtOne

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Learn a concept. Solve a problem. Build something real. Your next chapter starts here.

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BUILD YOUR FOUNDATION

A little structure.
A lot of possibility.

Go beyond memorizing answers. Build a deeper understanding through connected lessons, hands-on practice and checkpoints along the way.

Learn the idea.
Put it into practice.

16learning paths
0completed

Learn at your own pace

Find your next learning path

16 paths to explore

Beginner

Data Structures & Algorithms

Build strong algorithmic foundations, trace algorithms visually, solve progressive DSA problems, and apply invariants in real repository and code-review exercises.

231.7 hours279 lessons67 problems15 visualizers
Explore the curriculum
Arrays & StringsLinked ListsTrees & GraphsSorting & SearchingDynamic ProgrammingRecursion & BacktrackingBit ManipulationAdvanced Data Structures
Ready when you are
Start learning
Intermediate

High-Level System Design

Move from architecture fundamentals to concrete system-design cases, then test consistency, failure recovery and authorization decisions through repository coding and review.

268 hours268 lessons51 problems
Explore the curriculum
Scalability and reliabilityDistributed systemsStorage and databasesCaching and performanceMessaging and eventingSecurity and observabilityCloud architectureSystem design interviews
Ready when you are
Start learning
Intermediate

Low-Level System Design

Learn object-oriented design and design patterns, solve low-level design cases, and practise state transitions, persistence and error handling in real repositories and code reviews.

209.9 hours246 lessons44 problems
Explore the curriculum
Object-oriented designSOLID principlesDesign patternsAPI and persistence designConcurrency fundamentalsClean architectureTesting and maintainabilityLLD interview preparation
Ready when you are
Start learning
Intermediate

Database Management Systems

Study relational design, SQL, transactions and storage, reinforce query concepts with SQL problems, and apply consistency and analytical exports in repository coding and review.

221.4 hours252 lessons26 problems
Explore the curriculum
Relational ModelSQL MasteryER ModelingNormalizationTransactions & ACIDIndexing & B-TreesQuery OptimizationDistributed Databases
Ready when you are
Start learning
Intermediate

Computer Networks

Master Computer Networks from fundamentals to advanced protocols. This comprehensive path covers the OSI model, TCP/IP, routing, switching, network security, and modern networking with 46 chapters and 1200+ pages.

200 hours240 lessons
Explore the curriculum
OSI & TCP/IP ModelsEthernet & SwitchingIP Addressing & SubnettingRouting ProtocolsTransport Layer (TCP/UDP)Application ProtocolsNetwork SecurityWireless Networks
Ready when you are
Start learning
Intermediate

Operating Systems

Master Operating Systems from fundamentals to advanced concepts. This comprehensive path covers processes, threads, memory management, file systems, I/O, virtualization, and distributed systems with 47 chapters and 1201+ pages.

196.8 hours236 lessons
Explore the curriculum
Process ManagementThread SynchronizationMemory ManagementVirtual MemoryFile SystemsI/O SystemsVirtualizationDistributed Systems
Ready when you are
Start learning
Advanced

Machine Learning

Learn the mathematical and engineering foundations of machine learning, explore executable visualizers, implement algorithms, and validate dataset releases in repository exercises.

252.3 hours277 lessons39 problems12 visualizers
Explore the curriculum
Linear Algebra & CalculusProbability & StatisticsSupervised LearningUnsupervised LearningNeural NetworksDeep LearningReinforcement LearningML Engineering
Ready when you are
Start learning
Intermediate

Data Structures & Algorithms Patterns

Master Data Structures and Algorithms through 15 chapters of coding patterns. From Two Pointers to Dynamic Programming, this path covers 320 carefully curated problems organized by technique for optimal learning progression.

174.3 hours26 lessons323 problems15 visualizers
Explore the curriculum
Two Pointers & Sliding WindowBinary Search TechniquesStack & Queue PatternsTree & Graph AlgorithmsGreedy AlgorithmsBacktrackingDynamic ProgrammingBit Manipulation
Ready when you are
Start learning
Advanced

Machine Learning Patterns

Master Machine Learning from fundamentals to advanced techniques through 19 comprehensive chapters. This path covers 318 carefully curated problems spanning linear algebra, probability, classical ML, deep learning, reinforcement learning, and more.

155.6 hours15 lessons317 problems15 visualizers
Explore the curriculum
Linear Algebra & CalculusProbability & StatisticsClassical ML AlgorithmsNeural NetworksDeep LearningReinforcement LearningNLP & Computer VisionMLOps & Deployment
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Start learning
Beginner

SQL Practice: Queries to Analytics

Progress from filtering and joins to analytical windows, time-series queries and recursive SQL, with focused database lessons and a data-export repository capstone.

149.2 hours3 lessons305 problems
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SELECT, WHERE, ORDER BYJOINsGROUP BY and aggregationSubqueries and CTEsWindow functionsQuery optimization
Ready when you are
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Intermediate

Algorithms in Real Systems

Connect arrays, strings, graphs and scheduling to repository bugs and code-review decisions. Trace a small problem first, then apply the same invariant to a working service.

13.7 hours8 lessons15 problems2 visualizers
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Boundary conditions and ordered eventsIntervals and peak resource usageDependencies and propagationStrings and counted requirements
Ready when you are
Start learning
Intermediate

Backend Engineering Foundations

Learn the networking, data and object-design ideas behind a service, then implement and review authorization, state transitions and recovery in real repositories.

15.3 hours16 lessons12 problems
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From HTTP to service boundariesData and domain modelsAuthorization and policyTransactions and error recovery
Ready when you are
Start learning
Advanced

Reliable Services & Transactional Workflows

Practise retries, atomic writes, stale updates and scheduled actions through system-design cases and repository coding paired with review.

15.2 hours11 lessons14 problems
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Consistency and concurrent stateAtomic commits and recoveryAsynchronous deliveryTime boundaries and auditability
Ready when you are
Start learning
Intermediate

Data Quality & Analytics Engineering

Combine SQL reporting, data preparation and dataset-release controls. Work through correctness at boundaries, time-window exports and quality gates.

16.6 hours8 lessons26 problems
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Prepare trustworthy inputsQuery and aggregate correctlyTime windows and reproducible exportsRelease gates and production architecture
Ready when you are
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Intermediate

Repository Debugging & Code Review

Start with a small boundary bug, then progress through validation, authorization, ordering, transactional recovery and publication. Each implementation is paired with a focused code-review challenge.

18.1 hours2 lessons22 problems
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Find a boundary bugValidate and protect inputsCheck policy and stale stateTrace ordering and aggregationRecover atomically
Ready when you are
Start learning
Intermediate

Computer Science Interview Foundations

Review the essential algorithms, operating systems, networks, databases and design concepts, with representative implementation and design practice.

16.5 hours25 lessons12 problems1 visualizers
Explore the curriculum
Algorithms and complexityProcesses and concurrencyNetworks and requestsData and consistencyDesign, implement and explain
Ready when you are
Start learning