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One topic per page, nothing shouting for attention. Each lesson teaches from zero — with diagrams, real-world examples, and “where you’ll use it”. Start here.

✅ Live lessons

DSA · FoundationsBig-O ThinkingHow to tell fast code from slow before you run it.
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DSA · Pattern 1Arrays & HashingArrays, ArrayList, hashmaps, and “remember what you’ve seen”.
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DSA · Pattern 2Two PointersSolve pair/palindrome problems with no extra memory.
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DSA · Pattern 3Sliding WindowRuns, streaks, and “last N” — without re-scanning.
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DSA · Pattern 4Binary SearchHalve a sorted range — a million items in ~20 steps.
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DSA · Pattern 5Linked ListsNodes and pointers; reverse, merge, cycle detection.
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DSA · Pattern 6Recursion & BacktrackingFunctions that call themselves; the call stack; backtracking.
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DSA · Pattern 7Trees & BFS/DFSBranching data; depth-first vs breadth-first.
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DSA · Pattern 8Heaps & GreedyPriority queues; top-K; when greedy works.
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OOP · CoreOOP — The 4 PillarsEncapsulation, abstraction, inheritance, polymorphism — with real examples.
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SQL · CoreSQL JoinsTables, keys, and the 4 join types.
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SQL · CoreSQL IndexesWhy a query is slow — and the fix.
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SQL · CoreSQL TransactionsAll-or-nothing, ACID, and the money race.
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Java · CoreJava CollectionsList, Set, Map, Queue — and when to use each.
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Java · CoreExceptionstry/catch/finally; checked vs unchecked.
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Java · CoreGenericsType-safe code and those <angle brackets>.
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LanguagesC# — Java’s cousin~90% the same as Java; the differences that matter.
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Backend · APIs.NET — where C# runsCLR, NuGet, ASP.NET = the C# Spring Boot.
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Backend · APIsAPIs & RESTEndpoints, HTTP methods, status codes, JSON.
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Backend · APIsAuthenticationAPI keys, sessions, and how JWT works.
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SQL · CoreNormalizationStore each fact once; 1NF/2NF/3NF.
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🔨 Build · Project 1Recon — Reconciliation EngineYour defensible headline project.
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Go deeper — the full Library

Every track — Core Java, Spring Boot, SQL, Networking, System Design, Docker and more — now lives natively inside the app. No external sites.

Reference📚 The Library — 16 tracks, 150+ modulesAll native, one app. Follow the recommended path.
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These native lessons are the fastest interview path; the Library is the full curriculum for depth.

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