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Phase 1 — Foundations
Start here. Build strong fundamentals before jumping to systems.
Beginner
🌐How the Internet Works
IP, DNS, TCP/IP, HTTP/HTTPS basics. What happens when you type a URL.
🔌TCP vs UDP
Reliable vs fast delivery. When to use which. Three-way handshake.
🗄️SQL vs NoSQL
Relational vs document/key-value/graph. ACID vs BASE. When to choose what.
📇Database Indexing
B-tree indexes, covering indexes, when indexes hurt. Query optimisation.
⚡Caching Fundamentals
Why cache? Cache-aside, write-through, write-back. LRU, LFU. Redis basics.
🏗️OOP Principles (4 Pillars)
Encapsulation, Abstraction, Inheritance, Polymorphism with real examples.
🔩SOLID Principles
SRP, OCP, LSP, ISP, DIP. The backbone of every LLD interview answer.
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Phase 2 — Core HLD Building Blocks
The 10 concepts that appear in almost every system design interview.
Beginner–Intermediate
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Phase 3 — LLD & Design Patterns
Object-Oriented design, all 23 GoF patterns, SOLID in practice.
Intermediate
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Phase 4 — Intermediate System Design
Design real products end to end. Learn the tradeoffs.
Intermediate
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Phase 5 — Advanced System Design
Distributed systems at scale. The problems that separate senior engineers.
Advanced
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Phase 6 — Distributed Systems Deep Dive
Internals of databases, consensus, and large-scale infrastructure.
Advanced