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Lessons (20)

• Storage Engines & Database Operations

  … a bounded pool protects the primary while WAL, backups and replicas provide recoverability](/img/database/storage-operations.svg …

• Behavioral Patterns II: Chain, Template, Iterator, Mediator, Memento, Visitor

  … 2), mul(num(3), num(4))); walk(evaluate)(expression); // 14 walk(print)(expression); // "(2 + 3 × 4)" You've …

• O — Open/Closed Principle

  … method === "crypto") { return coinbase.charge(order.total, order.wallet); } // Next month: Apple Pay → edit again. Then Klarna → edit …

• The L6 System-Design Thinking Loop

  … design. 3. Name the first peak bottleneck. 4. Walk one crash, timeout, or retry. 5. Explain metrics, mitigation …

• How Browsers Render a Page

  … 4. Measure where every wall goes ( layout ). 5. Paint the walls ( paint ). 6. Stack the floors together ( composite …

• N+1 Queries, Loading & Pagination

  … Ask which fields the endpoint truly renders. Offset versus cursor pagination Offset asks the database to walk past …

• Behavioral Patterns I: Observer, Strategy, Command, State

  … Strategy 🗺️ Analogy: Google Maps offers routes by car, bike, walking or transit. Same goal (get from A …

• ACID, Transactions & Locks

  … success A committed payment record is recovered from WAL/replication. Consistency is not a promise that every replica …

• D — Dependency Inversion Principle

  … It has a plug , and the wall has a socket . Both depend on a shared standard, the socket …

• Comments & Formatting

  … save(html) { / … / } Blank lines separate ideas js // ❌ A wall of text function checkout(cart){const total=sum(cart …

• Linked Lists

  … Access i-th element O(1) O(n): walk from the head Insert/delete at start O(n …

• Two Pointers & Sliding Window

  … They meet in the middle having checked everything in one pass . ![Two pointers walking toward each other on …

• Arrays & Strings

  … Because the lockers are side by side and numbered, you can walk straight to locker 42 without opening …

• Layered (N-Tier) Architecture

  … A customer never walks into the storeroom, and the storeroom never talks to customers. Each layer only talks …

• DSA Interview Patterns Cheat Sheet

  … Code<br/ clean names"] -- T["6️⃣ Test<br/ walk through"] -- X["7️⃣ Complexity<br/ time + space"] 1. Understand …

• Big-O Notation Made Simple

  … Double the houses, double the work. - O(n²): at every house, you walk back to visit every other …

• Creational Patterns: How to Make Objects

  … 5, abilities: ["walk", "attack"], describe() { return ${this.type}: ❤️ ${this.health}, 🏃 ${this.speed} ; }, }; // Clone the prototype, then change only …

• Vertical Slice Architecture & the Modular Monolith

  … Neighbours can't walk into each other's kitchens; they knock (a public interface). A modular monolith is …

• Caching & Redis

  … the things you use every day (keys, phone, wallet) on your desk , not in the basement storage room …

• Domain-Driven Design: Strategic Design

  … domain experts and developers put orange sticky notes on a long wall, one for every domain event (something …