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Dashboard
Week — · Target: Google
MISSION
"In the intersection of logic and creativity lies true innovation."
Technologist driven by the impulse to create. Architecting systems at VIT Chennai.
Roadmap
0%
Phase 1 of 6
LeetCode
Connect LeetCode
GitHub
Connect GitHub
CF Rating
Connect Codeforces
COGNITIVE LOAD ANALYST
Productivity Recommendation
AI // ONLINE
OPTIMIZATION
High
Sprinting Phase
Analyzing your trajectory... Current LeetCode consistency suggests you should pivot to **System Design (Phase 3)** to maximize your retention window. Focus on **Concurrency** patterns today.
SYSTEM DIAGNOSTICS
UPTIME
0h 0m
COGNITIVE MEMORY
20.0%
Daily Mastery Checklist
2 LeetCode Mediums
Review 1 System Design Pattern
30m Tech Fundamental Reading
Update Journal / Reflection
Practice 1 Behavioral (STAR) Story
Analyze 1 Tech Blog (Engineering Feed)
Open Source Contrib / Bug Hunting
System Design Mock Sketch
Quick Jumps
Tech Intelligence
Live Global Industry Pulse
Today's Schedule
Deep Focus
Start Sprint
25:00 Pomodoro Protocol
Quick Intel
Profile
PIYUSH KUMAR · VIT CHENNAI
Academic Profile
COLLEGE
V.I.T CHENNAI
BATCH
2025 — 2029
AMBITION
SOFTWARE FIELD · GAME DESIGNER · WEB-TOOL
Languages Learnt
PYTHONCC++HTMLSQL
Contact Information
INSTAGRAM@piyush_kumar
OS Personalization
CORE THEMES
SYSTEM COGNITION
Intelligence Index 842
Processing state: STABLE // Optimization: ACTIVE
Projects
System implementations
AI Research Hub
Global search and AI integration for personal knowledge management.
System Infrastructure
Cloudflare R2D1 SQLWorkers
Quantum Arcade
multi-game platform with shared economy and persistent progress.
Canvas APIState Machine
Cloud Vault
Secure storage for resumes, code snippets, and private study materials.
Supabase StoragePostgreSQL
Cloud Vault
Secure storage & document management
Root
☁️
Secure Upload Zone
Drag & drop files here or click to browse
🔍
Placement Guide
Comprehensive FAANG Handbook
1. Understanding the Giants
PHILOSOPHY
Google: Algorithmic complexity & scale.
Amazon: Leadership Principles & Ownership.
Meta: Fast iteration & Product Sense.
Apple: Precision & Security.
LEVELING
L3 (Junior/New Grad)
L4/L5 (Senior/LMM)
L6+ (Staff/Principal)
2. DSA Mastery — Pattern Guide
Structures Deep-Dive
  • Monotonic Stack: Next Greater Element problems.
  • Trie: Prefix matching & Dictionary search.
  • Segment Tree: Range queries (Sum/Min/Max).
  • Union-Find: Cycle detection & Disjoint sets.
Algorithmic Logic
  • Sliding Window: Subarrays/Substrings (O(n)).
  • Two Pointers: Sorted arrays (O(n)).
  • Backtracking: N-Queens, Sudoku, Subsets.
  • DP: Memoization vs Tabulation.
3. System Design — Architecture
CASE: URL SHORTENER

Hashing: Base62 encoding for IDs.

DB: NoSQL (Key-Value) for scale.

Cache: Redis for high-read redirecting.

CASE: CHAT SYSTEM

Protocol: WebSockets for bi-directional.

Offline: Message queuing (Kafka).

Status: Heartbeat mechanisms for presence.

Concepts: CAP Theorem (Consistency vs Availability), Load Balancers (Round Robin vs Least Conn), Database Sharding.
4. Advanced Technical Stack
DISTRIBUTED SYSTEMS
Microservices, Service Discovery, Fault Tolerance (Circuit Breakers), Consensus (Raft/Paxos).
CLOUD & DEV SEC
Docker/K8s, CI/CD pipelines, AuthN/AuthZ (OAuth2/JWT), OWASP Top 10.
5. Behavioral Question Bank

Conflict: Tell me about a time you disagreed with a peer.

Failure: Describe a project that didn't go as planned.

Impact: When did you take initiative above your role?

Adapt: How did you handle a drastic requirement change?

6. Impact Resume
  • Action Verbs: +Impact/Metrics.
  • Numbers: "Scaled to 1M requests".
  • Length: 1 Page strict.
7. Process
  • • 1. Recruiter Screen
  • • 2. Phone Screen
  • • 3. Onsite (4-6 rounds)
8. Platforms
LeetCode, HackerRank, InterviewBit.
9. Mocking
Pramp, Interviewing.io, Peer Mocks.
Strategy
Elite Preparation Framework
Behavioral — STAR Method

Situation: Context of the event.

Task: What was required of you?

Action: What did YOU specifically do?

Result: Outcome with numbers (e.g., +20% efficiency).

Target: Prepare 10-12 core stories.
Selection Differentiators
  • • Structured communication > Fast coding.
  • • Explaining trade-offs (A vs B).
  • • Handling ambiguity with clarifying questions.
  • • Writing modular, production-grade code.
Core Fundamentals
OS
Threads, Deadlocks, Mutex, Paging.
DBMS
Indexing, ACID, Query Optimization.
Networking
TCP/UDP, HTTP, Load Balancing.
X. TECHNICAL ARCHIVE (ADVANCED)
Distributed Computing Mastery

1. Consistent Hashing: Crucial for horizontal scaling. Solves the issue of re-mapping keys when nodes are added/removed. Ring structure with virtual nodes ensures uniform data distribution.

2. Gossip Protocols: Decentralized communication. Used for cluster membership and failure detection (e.g., Apache Cassandra, Redis Cluster).

3. Distributed Tracing: Observability in microservices. OpenTelemetry, Jaeger, and Zipkin. Context propagation across service boundaries.

4. Stream Processing: Kappa vs Lambda Architectures. Exactly-once processing guarantees in Apache Flink and Kafka Streams.

5. CAP Theorem & Trade-offs: Understanding when to prioritize Availability (AP) vs Consistency (CP) in systems like DynamoDB vs MongoDB.

6. Database Indexing Deep Dive: B-Trees vs B+ Trees, LSM Trees (Log-Structured Merge-Trees) for write-heavy workloads like Cassandra and InfluxDB.

High-Level Mental Models

1. First Principles Thinking: Breaking down complex problems into basic truths for innovation.

2. Pareto Principle (80/20): Focus on the 20% of patterns that cover 80% of LeetCode hard problems.

3. Second-Order Thinking: Considering the consequences of consequences (critical for System Design trade-offs).

4. Occam's Razor: Choosing the simplest architecture that solves the scale requirement.

Hard Algorithmic Patterns

• Heavy Hitters (Top K): Count-Min Sketch for frequency estimation. Misra-Gries algorithm for space-efficient top-k identification.

• Range Minimum Query (RMQ): Sparse Table (pre-processing O(N log N), query O(1)). Useful for LCA of trees.

• Network Flow: Ford-Fulkerson and Edmonds-Karp. Applications in bipartite matching and resource allocation.

• Advanced DP: DP on Trees (using DFS to propagate states), Digit DP (counting numbers with specific properties), Bitmask DP for TSP-style problems.

• Geometry Algorithms: Convex Hull (Monotone Chain), Segment Intersections, Sweep Line algorithms for range searches.

52-WEEK MASTER CURRICULUM

Week 1-4: Foundations & Logic. Big-O, Arrays, Strings, Two Pointers, Sliding Window.

Week 5-8: Core Structures. Linked Lists, Stacks, Queues, Recursion mastery.

Week 9-12: Hierarchical Data. Binary Trees, BSTs, Heaps, Treaps.

Week 13-16: Graph Theory. BFS, DFS, Connectivity, Topological Sort.

Week 17-20: Advanced Graphs. Dijkstra, Bellman-Ford, Prim's, Tarjan's SCC.

Week 21-26: Dynamic Programming. 1D, 2D, Knapsack, LIS, LCS, Matrix Chain.

Week 27-30: String Algorithms. KMP, Rabin-Karp, Z-Algorithm, Tries, Suffix Trees.

Week 31-35: System Design Fundamentals. Load Balancers, Proxies, Caching, Sharding.

Week 36-40: Advanced Systems. Microservices, Message Queues (Kafka), Consensus (Raft).

Week 41-45: Industrial Case Studies. Instagram, WhatsApp, Uber, Netflix, YouTube architecture.

Week 46-48: Behavioral Mastery. Leadership Principles, Conflict Resolution, STAR Method.

Week 49-52: High-Pressure Mocks. Peer interviews, Salary negotiation, Final Review.

"Consistency is the only superpower that matters."
Integrations
Connect your platforms — data is per-account
My Profiles
Live stats from your connected platforms
Activity Feed
Live Activity
Unified feed from all platforms
AI Coach / Analyst
Your personal technical co-pilot powered by Llama 3
System Initialized. I am your technical coach. What would you like to build or break today?
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AI Hub
The Most Famous Apps in the AI Ecosystem
LLMs & Intelligent Chat
Software Engineering
Creative & Multimedia
Research & Productivity
Specialized Industrial AI
Data Science: Polymer, Akkio, MonkeyLearn, KNIME, DataRobot.
Design/UI: Galileo AI, Uizard, Attention Insight, Fontbolt.
Marketing: Jasper, Copy.ai, Anyword, AdCreative, Writesonic.
Sales/CRM: Apollo.io, Gong, Lavender, Regie.ai, Outreach.
Customer Support: Intercom Fin, Ada, Kustomer, Forethought.
Legal: Harvey, CoCounsel, Ironclad, Luminance, Spellbook.
Deep Dev & Architecture AI
Code Reviews: Codacy, CodeRabbit, Codiga, DeepSource.
Documentation: Mintlify, Swimm, Trelent, scribe.
Testing: Applitools, Testim, Mabl, Functionize.
Security: Snyk AI, Mend.io, Checkmarx, Veracode.
Infrastructure: Pulumi AI, Firefly, Brainboard.
Omni-Productivity & Automation
Meetings: Otter.ai, Fireflies, Grain, Rewatch.
Email: Superhuman, Shortwave, SaneBox.
Workflows: Zapier Central, Make.com, Bardeen.
Visualizations: Gamma, Beautiful.ai, Tome, Decktopus.
Production Workflow
State-of-the-Art Stack & Orchestration
Category Recommended Stack Experience Review / Intel Like
Logic & Coding
AI Pair Programming
Claude 3.5 + Antigravity
Optimal for rapid iteration
Tried It
Backend & DB
Data Persistence
Cloudflare D1 (SQL)
SQLite-based Edge DB
Mark Tried
Deployment
Hosting Infrastructure
Cloudflare Pages
Global Edge Hosting + CI/CD
Tried It
Domain & DNS
Traffic Routing
Cloudflare
Fastest DNS propagation
Mark Tried
Payments
Revenue Systems
Stripe / LemonSqueezy
Global checkout logic
Mark Tried
Version Control
Git Architecture
GitHub
Branching/Actions workflows
Tried It
Auth
Identity & Sessions
Cloudflare Turnstile / KV
Google OAuth + Cookies
Tried It
Observability
Error Tracking
Sentry / LogRocket
Crash reports & sessions
Mark Tried
Reflection Checklist
Is it liked by me?
Overall stack satisfaction
Production Ready?
Battle-tested for users
Roadmap
Learning Path
AI Skills & Importance Matrix
Tiered curriculum from Junior to Staff Engineer.
Tier 1: Junior/Entry
Foundations of utility.
• Prompt Engineering mastery
• Basic API integration (OpenAI/Groq)
• Understanding LLM limitations (Hallucinations)
Tier 2: Mid/Senior
Building production systems.
• **RAG Pipelines**: Vector DBs & Retrieval
• Context Window management
• Agentic Workflows (Tool calling)
Tier 3: Staff/Architect
Strategic AI infrastructure.
• Multi-agent Orchestration (LangGraph)
• LLM Fine-tuning & Distillation
• AI Security & Compliance (Guardrails)
Advanced Resources
AI Blueprints
Production-ready workflows for AI-native applications.
Workflow: RAG Pipeline
Advanced Document Retrieval
1. **Ingest**: PDF/Text processing with chunking.
2. **Embed**: Generate vectors via `text-embedding-3`.
3. **Store**: Index in Pinecone or pgvector.
4. **Retrieve**: Semantic search for top-k chunks.
5. **Augment**: Feed context to LLM for final answer.
Workflow: Agentic Loop
Autonomous Problem Solving
1. **Plan**: LLM decomposes goal into sub-tasks.
2. **Execute**: Call tools (Search, Code Exec, DB).
3. **Verify**: Self-correction based on tool results.
4. **Iterate**: Loop until termination criteria met.
Operational Best Practices
• **Evaluations**: Use `Ragas` for retrieval quality.
• **Cost**: Implement token-based rate limiting.
• **Latency**: Use streaming for responsive UX.
Calendar
Study sessions · Google Calendar sync
MON
TUE
WED
THU
FRI
SAT
SUN
This Week's Schedule
Upcoming Sessions
🤖 AI Study Planner
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Progress
Heatmap · Journal · Phase breakdown
Activity Heatmap — 6 Months
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Phase Progress
Journal
AI Coach
Groq API · Fastest inference · 6,000 TPM free
Model Selection
📋 Review my LeetCode approach for Two Sum
🏗 Explain URL shortener system design
🤖 What AI/ML skills matter most for FAANG?
📝 Help me write a STAR leadership story
🧠 Explain Transformers simply
💼 Give me a mock behavioral question
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AI System Blueprints
Architectural templates for modern intelligence.
LLM RAG Pipeline
High-performance vector search architecture.
• **Ingestion**: Unstructured data -> Chunking -> Embeddings.
• **Retrieval**: Vector DB (Pinecone/Milvus) with semantic search.
• **Augmentation**: Context injection into LLM prompts.
Agentic Workflows
Autonomous multi-agent systems.
• **Planning**: Chain-of-Thought (CoT) and ReAct patterns.
• **Execution**: Tool use, function calling, and API integration.
• **Memory**: Persistent state across agent steps.
Intelligence Library & AI Skills
Curated resources and dynamic skill tracking.
My AI Skill Matrix
Recommended Learning Path
DSA Masters
The fundamental pillars of coding interviews.
System Design
Architecting at FAANG scale.
AI & ML Ops
Productionizing intelligence.
Career & Soft Skills
The "STAR" behind the engineer.
The Elite Intelligence Index (2026 Edition)
The most powerful technical and behavioral repositories on the web.
SYSTEM DESIGN (ARCHITECT)
Q: How do you design a URL shortener (TinyURL)?
A: Key components: Hash/Base64 encoding, NoSQL for high throughput (Key-Value), Redis cache for hot URLs, and a Redirection service. Use consistent hashing for scaling.
Q: Explain the difference between Push vs Pull in Notification systems.
A: Push: Server initiates (WebSockets/SSE); low latency but hard to scale with millions. Pull: Client polls periodically; easier to scale but introduces lag and overhead. Use Push for real-time.
Q: What is the "Thundering Herd" problem?
A: When many processes wake up to a single event (e.g., cache expiry) and crash the backend. Solve with: Jitter (random expiry), Mutex locks, or Probabilistic early expiration.
AI & ML ENGINEERING
Q: What is the difference between RAG and Fine-tuning?
A: RAG (Retrieval-Augmented Generation) provides external knowledge at inference; best for dynamic info. Fine-tuning updates model weights; best for learning style, domain-specific terminology, or new capabilities.
Q: Explain "Temperature" in LLM sampling.
A: Controls randomness. T=0 is deterministic (picks max probability). Higher T (e.g., 0.7-1.0) flattens the distribution, allowing for more "creative" or diverse token selection.
Q: What is a Vector Database?
A: A database optimized for high-dimensional embedding storage and similarity search (ANN search). Essential for RAG. Examples: Pinecone, Weaviate, Milvus, Chroma.
CLOUD & INFRASTRUCTURE
Q: What is "Cold Start" in Serverless (FaaS)?
A: The latency when an idle function is invoked and the cloud provider must spin up a new container instance. Mitigate with: "Warm" pings, provisioned concurrency, or smaller code bundles.
Q: Explain Infrastructure as Code (IaC) - Declarative vs Imperative.
A: Declarative (Terraform/CloudFormation): Define the "Desired State". Imperative (Ansible/Scripts): Define the "Steps" to reach a state. FAANG prefers Declarative for reproducibility.
Q: How does a Content Delivery Network (CDN) work?
A: Caches static content at "Edge Locations" geographically closer to users. Uses Anycast routing to direct users to the nearest node, reducing latency and origin server load.
SECURITY & DEVSECOPS
Q: What is SQL Injection (SQLi) and how to prevent it?
A: Malicious SQL code injected into inputs. Prevent using **Prepared Statements** (Parameterized Queries) and input sanitization. Never concatenate raw strings into SQL.
Q: Explain Cross-Site Scripting (XSS).
A: Injecting malicious scripts into web pages viewed by other users. Mitigate with: CSP (Content Security Policy), HTML escaping, and "HttpOnly" cookies to prevent token theft.
Q: What is "Zero Trust" architecture?
A: A security model that assumes no actor (internal or external) is trusted by default. Requires continuous verification through MFA, identity-based access, and micro-segmentation.
ADVANCED SYSTEMS (L6+)
Q: Explain the CAP Theorem.
A: In a distributed system, you can only pick 2 of: Consistency, Availability, Partition Tolerance. Since network partitions are inevitable, real-world choices are CP or AP.
Q: What is "Eventual Consistency"?
A: A consistency model where, given no new updates, all accesses will eventually return the last updated value. Used in AP systems like DynamoDB or Cassandra for high availability.
Q: How does Consistent Hashing work?
A: Maps data and nodes to a circular hash ring. Minimizes data remapping when nodes are added or removed. Essential for scalable caches and distributed databases.
BACKEND & SYSTEMS
Q: Optimistic vs Pessimistic Locking.
A: Optimistic: Assume no collisions; use versioning (MVCC). Fast for read-heavy. Pessimistic: Lock resources immediately. Best for high-contention write-heavy scenarios.
Q: How does a B-Tree differ from an LSM Tree?
A: B-Tree: Optimized for Reads (RDBMS). LSM: Optimized for Writes (NoSQL). LSM uses Log-Structured merge-and-compact; B-Tree uses sorted nodes.
Q: What is an Inode in Linux?
A: Metadata structure storing file attributes (permissions, block pointers) but not the name/data.
The Hall of Fame: Legendary Interview Questions
The most iconic questions you MUST know to survive a FAANG interview.
"What happens when you type google.com?"
The Expert Answer:
1. **DNS Lookup**: Local cache -> Resolver -> Root -> TLD -> Authoritative.
2. **TCP/TLS Handshake**: 3-way TCP handshake + TLS 1.3 certificate exchange.
3. **HTTP Request**: Browser sends GET request via the socket.
4. **Server Processing**: Load Balancer -> Web Server -> App Server -> Database.
5. **Rendering Phase**: CRP (Parsing HTML/CSS -> Layout -> Painting on GPU).
"Design a Rate Limiter" (System Design)
The Expert Answer:
1. **Algorithm**: Token Bucket (best for burst traffic) or Leaky Bucket (smooth traffic).
2. **Storage**: Redis (fast in-memory increment/decrement).
3. **Strategy**: Sliding Window Log (precise) vs Fixed Window (simpler, but burst issues).
4. **Scaling**: Use Redis clusters and a centralized Rate Limiting service to avoid local state issues.
"Reverse a Linked List" (The DSA Classic)
The Expert Answer:
1. **Iterative**: Use three pointers: `prev`, `curr`, `next`. Move them step-by-step to flip the `next` pointer of `curr`.
2. **Recursive**: Base case (head is null or head.next is null). Recursive call to reverse the rest, then set `head.next.next = head` and `head.next = null`.
3. **Complexity**: Time O(N), Space O(1) iterative, O(N) recursive (stack).
"Two Sum" (The Legend)
The Expert Answer:
1. **Brute Force**: O(N^2) comparison.
2. **Optimized**: Use a Hash Map to store `complement = target - nums[i]`.
3. **Single Pass**: As you iterate, check if the current number's complement exists in the map. If not, add the current number and its index to the map.
4. **Complexity**: Time O(N), Space O(N).
BEHAVIORAL (STAR)
Q: "Tell me about a time you failed."
A: Focus on a genuine professional mistake, explain the immediate correction (Action), the lesson learned, and how you ensured it never happened again (Result). No "fake" failures.
Q: "What is your biggest weakness?"
A: Pick a technical skill or "soft" trait you previously lacked, detail the structured steps you've taken to improve (courses, feedback loops), and show current progress.
Q: "How do you handle a toxic teammate?"
A: Focus on Professionalism, Communication, and Escalation (if needed). Show empathy but maintain team velocity and mental safety as the priority.
Engineering Blogs (Real-time Intel)
♾️
Meta Eng
🔍
Google Dev
🎬
Netflix Tech
☁️
AWS Arch
🏠
Airbnb Eng
🚗
Uber Eng
💳
Stripe Eng
🐙
GitHub Eng
🧡
Cloudflare
👾
Discord Eng
💬
Slack Eng
📌
Pinterest
🔗
LinkedIn Eng
📦
Dropbox Tech
🎈
DoorDash
🚕
Grab Eng
🎨
Lyft Eng
🤖
Reddit Eng
🎧
Spotify Eng
🖌️
Canva Eng
Video Mastery Academy (Free Courses)
AI Arsenal & Tooling (Force Multipliers)
Claude 3.5 Sonnet
Pro-tier code architecture
Cursor IDE
The AI native VS Code fork
v0.dev
UI/UX generation by Vercel
Perplexity AI
Live web search & research
Phind
Developer search engine
ChatGPT Plus
GPT-4o & Canvas mastery
Google Gemini
Multimodal 1.5 Pro model
ElevenLabs
Industry leading AI voice
Runway Gen-3
High-end AI video generation
Leonardo.ai
Dynamic image/asset generation
Pika Art
Cinematic video motion
HeyGen
AI Avatar & Video translation
Quillbot
Paraphrasing & Writing aid
Grammarly
Real-time comms optimization
Otter.ai
Meeting notes & transcription
Fireflies
Intelligence for meetings
The 100+ Knowledge Index
System Architecture Vault
Distributed systems, scalability, and high availability.
Load Balancing
Distributing traffic across clusters.
• Algorithms: Round Robin, Least Conn, IP Hash
• Layer 4 vs Layer 7 balancing
• Health checks & auto-scaling
Caching Layer
Reducing latency with Redis/Memcached.
• Eviction: LRU, LFU, FIFO
• Strategies: Cache-aside, Write-through, Write-back
• Cache stampede prevention
Database Sharding
Horizontal scaling of data layers.
• Key-based vs Range-based sharding
• Re-sharding challenges
• Consistent Hashing
Message Queues
Asynchronous processing & decoupling.
• Pub/Sub vs Point-to-Point
• Kafka vs RabbitMQ vs SQS
• Idempotency in consumers
Interview War Room
Behavioral frameworks and technical drills.
STAR Method Framework
Structuring behavioral responses for impact.
S // Situation
Brief context of the challenge.
T // Task
What was your specific responsibility?
A // Action
The detailed steps YOU took.
R // Result
Quantified impact & outcome.
Behavioral Story Bank
Your vault of STAR-formatted career milestones.
The "Conflict" Story
S: Disagreement on system architecture with senior dev.
T: Resolve conflict without delaying the sprint.
A: Data-driven POC to compare throughput and latency.
R: Selected the hybrid approach; improved perf by 40%.
The "Ownership" Story
S: Production outage on Saturday midnight.
T: Restore service and find root cause.
A: Led the war room; identified faulty DB migration.
R: Stabilized in 2h; implemented pre-deploy checks.
The "Growth" Story
S: New team member struggling with the stack.
T: Onboard them effectively while hitting my goals.
A: Created 5-day bootcamp docs & pair programmed.
R: Independent contributor in 3 weeks; docs now standard.
+
Add New Success Story
Technical Drills
Focused exercises for high-stakes execution.
Coding Patterns Drill
Master the templates that solve 80% of problems.
Sliding Window
Subarrays, substrings, constraints
Fast & Slow Pointers
Cycle detection, linked lists
Merge Intervals
Scheduling, overlapping timeframes
Top K Elements
Heaps, frequency analysis
Mock Simulator
Simulate a high-pressure 45-minute round.
45:00
Level: SDE-II (Generalist)
• Peer-mode: Share screen with a friend
• AI-mode: Record & Analyze with AI Coach
• Performance Metrics: Speed, Quality, Edge Cases
Gmail
Recent emails from your connected account
📧
Connect Gmail to see your emails
Google Drive
Your files & study documents
📁
Connect Google Drive to access your files
The Success Protocol
Execution strategies for the high-stakes moment.
1. The Communication Protocol
Coding is only 50% of the score.
• **Think Aloud**: Narrate your logic before typing a single line.
• **Trade-off Analysis**: "I'm using a HashMap here to trade memory for O(1) time."
• **Edge Case Verification**: Before coding, list 3-5 edge cases (empty input, duplicates, etc).
• **Dry Run**: Manually trace your code with a small input after finishing.
2. Asking Smart Questions
Reverse the power dynamic.
• "How does the team handle technical debt vs new feature velocity?"
• "What does a successful first 90 days look like for someone in this role?"
• "How do you maintain system consistency across specialized squads?"
• "What's the most challenging architectural decision the team made recently?"
3. Day-of Preparation
The 24h Countdown Checklist
• **Environment**: Test your camera, mic, and internet stability.
• **Whiteboard**: Have a physical or digital canvas ready for sketching.
• **Hydration**: Water and light snacks only. Peak cognitive state required.
• **Mindset**: You are a consultant helping them solve a problem, not a student being tested.
4. The "Closing" Post-Interview
Master the follow-up.
• Send personalized thank-you notes referencing specific discussion points.
• Update your recruiter on any other interview timelines (urgent status).
• Reflect & Log: Immediately record every question asked in your FAANG OS journal.
Language Internals
Deep dives into the mechanics of your primary stack.
Java: The JVM Ecosystem & Platform Internals
JVM Memory Model (JMM)
• **Heap vs Stack**: Objects live on heap; local variables on stack. Understanding escape analysis.
• **Metaspace**: Post-Java 8 replacement for PermGen. Stores class metadata.
• **Native Memory**: Buffers (DirectByteBuffers) and JNI allocations outside JVM control.

Garbage Collection (GC) Evolution
• **G1 GC**: Region-based, predictable pauses via throughput/latency trades.
• **ZGC (JDK 15+)**: Sub-millisecond pauses by using colored pointers and load barriers.
• **Shenandoah**: Ultra-low pause GC by performing evacuation concurrently with application threads.

Concurrency & Synchronization
• **Project Loom**: Introduction of Virtual Threads (M:N scheduling) avoiding OS thread overhead.
• **Happens-Before Relationship**: Volatile, Synchronized, and Final semantics under JMM.
• **CAS Operations**: Compare-And-Swap internals (Unsafe API) for non-blocking algorithms.
Just-In-Time (JIT) Compilation
• **C1 (Client) vs C2 (Server)**: Tiered compilation strategies. HotSpot profiling.
• **Inlining & Devirtualization**: How the JVM removes method call overhead via profile-guided optimization.
• **AOT (GraalVM)**: Ahead-of-time compilation for instant startup in serverless environments.

Collections & Data Internals
• **HashMap Collision Strategy**: Treeify thresholds (O(log n) trees vs O(1) buckets).
• **ConcurrentHashMap**: Striped locking vs CAS for high-throughput thread safety.
• **CopyOnWriteArrayList**: Tradeoffs for read-heavy vs write-heavy workloads.

FAANG Interview High-Frequency Patterns
• Handling Deadlocks (Thread Dump analysis).
• Optimizing Serialization (Protobuf vs JSON performance).
• Custom ClassLoader implementation for plugin architectures.
JavaScript: V8 Engine & Runtime Mechanics
The V8 Pipeline
• **Ignition & TurboFan**: Interpreter to Optimizing Compiler lifecycle. De-optimization traps.
• **Hidden Classes (Shapes)**: How V8 treats dynamic JS objects like static structs for speed.
• **Inline Caches (IC)**: Speeding up property lookups by remembering previous search results.

Memory Management
• **Young Generation (Scavenge)**: Fast, semi-space based GC for short-lived objects.
• **Old Generation (Mark-Sweep-Compact)**: Triggered when objects survive multiple scavenges.
• **Memory Leaks**: Identifying closures, detached DOM nodes, and unintentional globals.
Concurrency Model
• **The Event Loop**: Microtasks (Promises) vs Macrotasks (setTimeout/I/O).
• **Web Workers**: Parallelism via OS threads, communicating via `postMessage`.
• **SharedArrayBuffer & Atomics**: High-performance shared memory patterns in JS.

Advanced Modern JS
• **Proxy & Reflect**: Intercepting and defining custom behavior for fundamental operations.
• **Temporal API**: Fixes to the legacy `Date` object (Immutable, Type-safe).
• **ESModules vs CJS**: Static analysis benefits and tree-shaking internals.
Python (CPython) Internals
• **Reference Counting**: The primary GC mechanism. Circular references handled by generational cyclic GC.
• **Global Interpreter Lock (GIL)**: Understanding the bottleneck in multi-core CPU-bound tasks.
• **Integer Interning**: Why `a is b` is true for small integers (-5 to 256).
• **Asyncio**: Cooperative multitasking via `yield from` and `await` internals.
Go (Runtime & GMP)
• **GMP Scheduler**: G (Goroutine), M (Machine/OS Thread), P (Processor/Context). Work-stealing algorithm.
• **Channels**: Under the hood — Hchan struct, lock-based wait queues for synchronization.
• **Slices**: Header structure (Pointer, Len, Cap). Understanding backing array sharing.
• **GC**: Concurrent Tri-color Mark & Sweep with short Stop-The-World (STW) phases.
Salary & Negotiation Vault
Master the art of the deal and secure your worth.
Negotiation Scripting
Scenario: The Initial Offer
"Thank you so much for the offer! I'm really excited about the team. Based on the market data for this role and my current interviews with X and Y, I was expecting something closer to Z. I'd love to see if there's flexibility on the base/equity."
Key Anchors:
• Never give a number first.
• Use competing offers as leverage.
• Focus on total compensation (TC), not just base.
Market Intel
🔗 Levels.fyi (TC Benchmarks)
🔗 H1B Data Info (Public Filings)
🔗 Blind (Insider Salary Threads)
Top Tier Benchmarks (L5/Senior)
Meta: $380k - $450k TC
Google: $350k - $420k TC
Netflix: $450k+ (All Cash preferred)
Engineering Journal
Log your Today-I-Learned (TIL) and technical musings.
Recent Entries
FEBRUARY 27, 2026
Understood the difference between Kafka's ISR and Ack strategies. Critical for data durability.
FEBRUARY 26, 2026
Deep dive into B+ Tree vs LSM Trees. LSM is optimized for writes; B+ for fast reads.
The Technical Nexus
A massive-scale encyclopedia of engineering knowledge.
Cloud & Distributed Patterns
Event Sourcing
State is stored as a sequence of immutable events. Enables perfect audit trails and "time travel" debugging. Use with **CQRS** for scalable read/write paths.
Saga Pattern
Manages distributed transactions across microservices. **Choreography** (events) vs **Orchestration** (central controller). Essential for consistency without locking.
Circuit Breaker
Prevents cascading failures. States: **Closed** (normal), **Open** (failing fast), **Half-Open** (probing). Implement with Hystrix or Resilience4j.
Sidecar Decorator
Deploy auxiliary features (logging, security, service mesh) in a separate container next to the app. Common in K8s (Envoy, Istio).
Bulkhead Isolation
Isolate resources (thread pools, memories) for different system parts. If one part fails, the others remain afloat.
Strangler Fig
Incrementally migrate a legacy system by replacing specific features with new services until the old system is completely "strangled".
Advanced Data Structures Compendium
Probabilistic Structures
Type Core Use Case
Bloom Filter Membership testing (Yes/Maybe). Zero false negatives.
HyperLogLog Cardinality estimation (Count distinct) with tiny memory.
Count-Min Sketch Frequency estimation in stream processing.
Performance Structures
Type Core Advantage
Skip List O(log N) search/insert. Simpler to implement than AVL/Red-Black.
LSM Tree Optimized for high-throughput write (used in NoSQL like ScyllaDB).
Merkle Tree Efficient verification of large datasets (Blockchain, Git).
Networking & Web Internals Deep Dive
Modern Web Protocols
• **HTTP/2**: Multiplexing, Binary protocol, HPACK compression, Server Push.
• **HTTP/3 (QUIC)**: Built on UDP. Eliminates Head-of-line blocking. Zero-RTT handshakes.
• **gRPC**: Protobuf serialization. Bi-directional streaming. Strong typing via IDL.
• **WebSockets**: Persistent full-duplex TCP connection for low-latency notifications.
• **SSE (Server-Sent Events)**: Uni-directional streaming from server to client over HTTP.
Low Level Networking
• **TCP 3-Way Handshake**: SYN -> SYN-ACK -> ACK. Reliable byte stream.
• **DNS Resolution**: Recurse -> Root -> TLD -> Authoritative. Cache at every level.
• **CDN Caching**: Edge locations. TTL management. Stale-while-revalidate.
• **TLS 1.3**: Handshake reduced to 1 round-trip. Forward secrecy by default.
Operating Systems Engine Room
Concurrency & Scheduling
• **Processes vs Threads**: Isolation vs Shared Memory. Context switch overhead.
• **Preemptive vs Cooperative**: OS-led vs App-led task switching.
• **Deadlocks**: Mutual Exclusion, Hold and Wait, No Preemption, Circular Wait.
• **Semaphores vs Mutexes**: Signaling vs Locking. Priority Inversion problems.
Memory Governance
• **Virtual Memory**: Paging and Segmentation. TLB (Translation Lookaside Buffer) for speed.
• **Page faults**: Mapping missing memory from disk. Swap space management.
• **Stack vs Heap**: LIFO automatic allocation vs Manual dynamic allocation.
• **Huge Pages**: Reducing TLB pressure for large databases (Postgres optimization).
System Design Mega-Checklist (50+ Points)
Reliability
[ ] Redundancy at all tiers
[ ] Rate Limiting (Token Bucket)
[ ] Circuit Breakers implemented
[ ] Failover mechanism tested
[ ] Idempotency keys in place

Scalability
[ ] Stateless app tier
[ ] DB Read Replicas
[ ] Horizontal Pod Auto-scaling
[ ] Partitioning (Sharding) key selection
[ ] CDN for static assets
Maintainability
[ ] Centralized Logging (ELK/Splunk)
[ ] Distributed Tracing (Jaeger/Zipkin)
[ ] Feature Flags for rollouts
[ ] Infrastructure as Code (Terraform)
[ ] CI/CD with automated rollbacks

Performance
[ ] Connection Pooling
[ ] Compression (Gzip/Brotli)
[ ] Async processing (Queues)
[ ] Index optimization (Covering indexes)
[ ] Batching requests
AppSec & Cryptography
Hardening systems and protecting data.
OWASP Top 10 Mastery
• **Injection**: SQLi, XSS, Command Injection prevention.
• **Broken Auth**: JWT security, session fixation, MFA bypasses.
• **Sensitive Data**: At-rest vs In-transit encryption.
• **SSRF**: Server-Side Request Forgery mitigation.
Modern Cryptography
• **Symmetric**: AES-256-GCM (Authenticated Encryption).
• **Asymmetric**: RSA vs Elliptic Curve (Ed25519).
• **Hashing**: Argon2, bcrypt (Salted & Peppered).
• **PFS**: Perfect Forward Secrecy in TLS handshakes.
SRE & Observability
Infrastructure as Code and Reliability Engineering.
The Golden Signals
• **Latency**: Time it takes to service a request.
• **Traffic**: Demand placed on the system.
• **Errors**: Rate of failed requests.
• **Saturation**: How "full" is your service?
Error Budgets (SLO/SLA)
Managing the tradeoff between velocity and stability. If current reliability > SLO, ship faster. Else, freeze deployments.
Staff Secret: Chaos Engineering

Deliberately injecting failure (Gremlin/Chaos Monkey) to reveal hidden weaknesses.

Data Engineering
Scalable pipelines and warehouse architecture.
ETL vs ELT
• **ETL**: Extract-Transform-Load (Traditional, Spark/Airflow).
• **ELT**: Extract-Load-Transform (Modern, Snowflake/BigQuery/dbt).
Storage Architecture
• **Data Lake**: Raw storage (S3/HDFS).
• **Warehouse**: Structured/Optimized (Redshift).
• **Lakehouse**: Hybrid approach (Databricks/Delta Lake).
Core CS Theory
The mathematical foundations of computation.
Complexity Theory
• **P vs NP**: The ultimate unsolved challenge.
• **NP-Hard & NP-Complete**: Identifying non-polynomial problems.
• **Space Complexity**: PSPACE, L, and NL classes.
Discrete Math
• **Combinatorics**: Permutations/Combinations for problem counting.
• **Grant Theory**: Isomorphism, Planarity, and Coloring.
• **Set Theory**: Venn diagrams, Power sets, and Cardinality.
Cloud Native & K8s
Orchestrating the global compute layer.
Kubernetes Internals
• **Control Plane**: API Server, etcd (Consensus), Scheduler, Controller Manager.
• **Node Components**: Kubelet, Kube-proxy, Container Runtime (containerd/CRI-O).
• **Networking**: CNI (flannel/calico), Services (ClusterIP/LoadBalancer), Ingress.
Serverless & Mesh
• **Service Mesh**: Istio/Linkerd for mTLS, traffic splitting, and observability.
• **FaaS**: AWS Lambda / Cloudflare Workers scaling from 0 to ∞.
• **Infrastucture as Code**: Terraform vs Crossplane (Control Plane for everything).
Quantum Computing
The frontier of computational physics.
Quantum Mechanics
• **Superposition**: Qubits existing in multiple states simultaneously.
• **Entanglement**: Correlation between qubits regardless of distance.
• **Interference**: Controlling probability amplitudes to amplify correct answers.
Algorithms & Security
• **Shor's Algorithm**: Exponentially faster prime factorization (Breaking RSA).
• **Grover's Algorithm**: Quadratic speedup for unstructured search.
• **Post-Quantum Crypto (PQC)**: Lattice-based and Isogeny-based defense.
Bio & HealthTech
Engineering the code of life.
Digital Health Standards
• **FHIR (HL7)**: Fast Healthcare Interoperability Resources (The API of Health).
• **DICOM**: The standard for medical imaging processing.
• **HIPAA/GDPR Compliance**: Security patterns for PHI (Protected Health Info).
Bioinformatics & AI
• **AlphaFold**: Decoding protein structures with deep learning.
• **Genome Sequencing**: Processing PBs of fastq data at scale.
• **Synthetic Bio**: Programming DNA using high-level CAD tools.
Hardware & Robotics
Building the physical substrate of intelligence.
Digital Logic & RTL
• **VHDL/Verilog**: Hardware Description Languages (HDL).
• **FPGA Design**: Prototyping logic on reconfigurable silicon.
• **ASIC Flow**: Synthesis, Place & Route, and Fabrication.
Robotics & Control
• **ROS 2**: Robot Operating System (The industry standard).
• **SLAM**: Simultaneous Localization and Mapping.
• **PID Control**: Feedback loops for motor/actuator precision.
Game Dev & Graphics
Crafting high-performance visual worlds.
Graphics Pipeline
• **Shaders (HLSL/GLSL)**: Vertex, Fragment, and Compute shaders.
• **Ray Tracing**: Real-time lighting simulations (RTX/DirectX Raytracing).
• **Vulkan/D3D12**: Low-level graphics APIs for maximum GPU control.
Game Engines
• **Unreal Engine 5**: Lumen, Nanite, and C++ gameplay architecture.
• **Unity**: C# scripting, ECS (Entity Component System) for performance.
• **Physics Engines**: Collision detection, rigid body dynamics (PhysX/Havok).
Web3 & Blockchain
Decentralized protocols and trustless code.
Smart Contracts
• **Solidity**: Ethereum Virtual Machine (EVM) development.
• **Rust (Solana)**: High-performance parallelized smart contracts.
• **DeFi Legos**: AMMs, Lending protocols, and Yield aggregators.
Consensus & Cryptoeconomics
• **PoS vs PoW**: Understanding Ethereum's Merge and Bitcoin's security.
• **L2 Scaling**: Optimistic vs ZK-Rollups (Arbitrum, StarkNet).
• **Zero Knowledge**: zk-SNARKs and zk-STARKs for absolute privacy.
Aerospace & Embedded
Mission-critical systems and zero-failure code.
Embedded Systems
• **RTOS**: Real-Time Operating Systems (FreeRTOS, Zephyr).
• **Bare Metal**: Writing C/Rust directly for ARM/Cortex-M.
• **Buses**: I2C, SPI, CAN bus (Automotive & Aero standard).
Avionics & Space
• **DO-178C**: Software considerations in airborne systems certification.
• **GNC**: Guidance, Navigation, and Control algorithms.
• **Telemetry**: Processing high-frequency sensor data streams.
Systems Internals
Mastering performance-critical systems programming.
C++: High Performance & Modern Architectures
Modern Memory Management
• **Move Semantics**: Rvalue references, `std::move`, and `std::forward`. Eliminating deep copies.
• **Smart Pointers**: `unique_ptr` (Exclusive), `shared_ptr` (Ref-counting), `weak_ptr` (Cycle breaking).
• **RAII Mastery**: Automating resource management (Sockets, Mutexes, Database handles) via destructor scopes.

Template Meta-Programming
• **SFINAE & Concepts**: C++20 standard for cleaner generic code constraints.
• **Variadic Templates**: Recursive compile-time unrolling for typesafe tuple/argument processing.
• **CRTP**: Curiously Recurring Template Pattern for static polymorphism.

Concurrency & Parallelism
• **Memory Ordering**: `memory_order_relaxed` vs `memory_order_seq_cst`. Tuning for multi-core scalability.
• **Atomics**: Lock-free programming internals using CPU instructions like CAS.
• **Executors & Senders/Receivers**: The future of structured concurrency in C++.
STL & Performance Architecture
• **Vector Internals**: Allocation strategies, capacity doubling, and cache locality benefits.
• **Unordered Containers**: Hash table implementation (Open addressing vs Chaining) in STL.
• **Custom Allocators**: High-frequency trading (HFT) patterns using Arena/Pool allocators to bypass heap fragmentation.

Low-Level & Hardware Interaction
• **SIMD**: Single Instruction, Multiple Data optimization (Intrinsics like AVX-512).
• **Cache Alignment**: Preventing "False Sharing" by padding structures to cache line size.
• **Branch Prediction**: Writing "Branchless" code for hot paths in critical systems.
C: Low-Level Mastery & OS Foundations
Memory & Pointers
• **Pointer Arithmetic**: Direct memory manipulation and buffer management.
• **The Matrix**: 2D/3D arrays vs pointer-to-pointers (Memory contiguousness trade-offs).
• **Type Punning**: Using `union` or pointer casting to reinterpret bit patterns (Common in Network Protocols).

OS Interface & System Calls
• **File Descriptors**: Everything is a file. The `dup2` and `pipe` dance for IPC.
• **Socket Programming**: Mastering `select`, `poll`, and the high-performance `epoll` edge-triggering.
• **Memory Mapping**: `mmap` for zero-copy I/O and shared memory segments.
Tools & Runtime
• **The Preprocessor**: Macro magic, X-macros, and conditional compilation guards.
• **Linkers & Loaders**: ELF format internals, PLT/GOT tables, and dynamic library resolution.
• **Valgrind & GDB**: Deep-dive debugging into segment faults and heap corruption.

Embedded & Optimization
• **Volatile Keyword**: Preventing compiler optimizations for memory-mapped I/O.
• **Inline Assembly**: Dropping to ASM for time-critical instructions.
• **Padding & Alignment**: How compilers align structure members to memory boundaries.
Rust: Safety & Performance
• **Ownership & Borrowing**: The Borrow Checker's role in zero-cost memory safety.
• **Fearless Concurrency**: How Send/Sync traits prevent data races at compile-time.
• **Cargo**: More than a package manager — managing reproducible builds and testing.
• **Unsafe Rust**: The escape hatch for FFI and manual memory management safely encapsulated.
The Design Lab (Staff+)
Solving elite-tier system design scenarios.
Scenario: Google-Scale Web Crawler
• **Scale**: 100+ Billion pages, highly dynamic content.
• **Key Challenges**: URL Frontier, Politeness service, Checksum deduplication.
• **Architecture**: Distributed worker nodes with local Bloom filters and global HBase storage.
Scenario: Uber Dispatch Service
• **Scale**: 1M+ active drivers, low-latency matching.
• **Key Challenges**: Geo-sharding (S2 cells / H3), Real-time state updates.
• **Architecture**: Peer-to-peer ring (Ringpop) for state management and high availability.
Scenario: Global Ad-Reporting
• **Scale**: 10B+ events per day, exact-once semantics.
• **Key Challenges**: Late arriving data, Deduplication, Real-time aggregation.
• **Architecture**: Kappa Architecture using Kafka, Flink, and Druid.
FinTech & HFT
Engineering for nanosecond precision.
Low Latency Engineering
• **Kernel Bypass**: Using DPDK/Solarflare for zero-copy networking.
• **Memory Layout**: Cache-line alignment and false sharing prevention.
• **Lock-Free Concurrency**: Atomic operations and memory barriers.
• **FIX/FAST Protocols**: The standards of financial data exchange.
Market Infrastructure
• **Matching Engines**: Order book management and priority sequencing.
• **Risk Controls**: Pre-trade checks and kill switches.
• **Compliance**: KYC/AML and financial auditing standards.
Mobile Mastery
Deep-dive into iOS & Android internals.
iOS Internals (Swift)
• **ARC (Automatic Reference Counting)**: Swift's unique memory model.
• **Grand Central Dispatch (GCD)**: Concurrency and Thread management.
• **UIKit vs SwiftUI**: Imperative vs Declarative UI paradigms.
• **LLVM**: The compiler backend powering iOS apps.
Android Internals (Kotlin)
• **ART (Android Runtime)**: AOT vs JIT compilation for bytecode.
• **Coroutines**: High-intensity asynchronous task management.
• **Jetpack Compose**: Modern reactive UI framework.
• **Binder IPC**: The heart of Android's process communication.
MLOps Foundry
Scaling and productionizing machine learning.
Model Training & Versioning
• **DVC (Data Version Control)**: Handling large datasets like code.
• **MLflow**: Tracking experiments, parameters, and metrics.
• **Kubeflow**: Running end-to-end ML workflows on Kubernetes.
Serving & Monitoring
• **Feature Stores**: Centralized storage for model inputs (Tecton/Feast).
• **Model Serving**: Triton Inference Server vs TensorFlow Serving.
• **Drift Detection**: Monitoring for concept and data drift in production.
Red Team Security
Offensive security and adversarial simulations.
Exploitation Frameworks
• **Metasploit**: Industry standard for vulnerability exploitation.
• **Cobalt Strike**: Leading platform for adversary simulations.
• **Cribling/Fuzzing**: Finding zero-days via automated input testing.
Social Engineering & Cloud Hacks
• **Phishing Campaigns**: Testing the human element of security.
• **IAM Escalation**: Pivoting through AWS/Azure roles.
• **Container Escape**: Breaking out of K8s/Docker environments.
Spatial Computing
Building the future of AR, VR, and XR.
3D Foundations
• **SLAM**: Simultaneous Localization and Mapping (The eyes of AR).
• **Scene Understanding**: Plane detection and occlusion mapping.
• **Spatial Audio**: HRTF (Head-Related Transfer Function) for 3D sound placement.
Frameworks & SDKs
• **Apple VisionOS**: RealityKit and ARKit mastery.
• **OpenXR**: The cross-platform standard for XR devices.
• **Stereo Rendering**: Optimizing for dual-display high-refresh outputs.
Cloud DevSecOps
Scaling security across the deployment pipeline.
Identity & Access
• **OAuth2 / OIDC**: Standardizing authentication across services.
• **Zero Trust**: "Never trust, always verify" network architecture.
• **SPIFFE/SPIRE**: Secure Production Identity Framework for workloads.
Hardened Pipelines
• **SAST/DAST**: Static and Dynamic security testing in CI/CD.
• **SCA**: Software Composition Analysis (Managing vulnerable deps).
• **Secret Scanning**: Preventing credential leaks (gitleaks/TruffleHog).
Incident Response
Managing critical failures with SRE precision.
The Incident Life Cycle
• **Detection**: SLI/SLO alerts and anomaly detection.
• **Triage**: Identifying the blast radius and severity (SEV 1-4).
• **Mitigation**: Traffic shifting, rollbacks, and capacity scaling.
Post-Incident Culture
• **Blameless Post-mortems**: Focus on system flaws, not human error.
• **5 Whys**: Root cause analysis framework.
• **Action Items**: Tracking long-term structural fixes to prevent recurrence.
DSA Mastery Roadmap
The absolute essentials for FAANG-level technical proficiency.
1. Core Data Structures
• **HashMaps**: O(1) average lookup. Essential for frequency & mapping.
• **Trees**: Heaps (Priority Queues), BSTs, and Trie (Prefix Tree).
• **Graphs**: Adjacency lists vs matrices. Essential for network problems.
• **Stacks & Queues**: BFS implementation and Monotonic Stack patterns.
2. Algorithmic Paradigms
• **Dynamic Programming**: Memoization vs Tabulation. Knapsack, LIS, LCS.
• **Backtracking**: N-Queens, Palindrome Partitioning, Sudoku Solver.
• **Binary Search**: Not just on sorted arrays! (Search in search space).
• **Greedy**: Sorting first is often the key. Interval problems.
3. The Big-10 Coding Patterns
1. **Two Pointers**: O(N) traversal.
2. **Sliding Window**: Subarray/Substring constraints.
3. **Fast & Slow Pointers**: Cycles & Midpoints.
4. **Merge Intervals**: Scheduling logic.
5. **Cyclic Sort**: Finding missing numbers.
6. **BFS/DFS**: Graph & Tree traversals.
7. **Top K Elements**: Heap-based optimization.
8. **K-way Merge**: Merging sorted datasets.
9. **Bit Manipulation**: Masking & XOR magic.
10. **Topological Sort**: Dependency resolution (DAGs).
4. Bit Manipulation Mastery
• **Check Power of 2**: `(n & (n-1)) == 0`
• **XOR Magic**: `a ^ a = 0`, `a ^ 0 = a`. Find unique element.
• **Count Set Bits**: Brian Kernighan's Algorithm.
• **Bit Masking**: Subset generation and flag management.
5. Mathematical Essentials
• Primes (Sieve of Eratosthenes)
• GCD/LCM (Euclidean Algorithm)
• Modular Arithmetic & Exponentiation
• Reservior Sampling (O(N) random pick)
Distributed Systems
Advanced consensus, consistency, and fault tolerance.
Consensus Algorithms
• **Raft/Paxos**: Leader election & log replication
• **2PC/3PC**: Atomic commitments in DBs
• **Quorum**: R+W > N requirements
Consistency Models
• **Strong Consistency**: Linearizability
• **Eventual**: Conflict resolution (CRDTs)
• **Causal**: Happens-before relationships
Fault Tolerance
• **Heartbeats**: Failure detection mechanisms
• **Replication**: Active vs Passive strategies
• **Idempotency**: Retrying with Unique Keys
PACELC Theorem
Beyond CAP
Latency vs Consistency trade-offs during normal operation.
Frontend Mastery
HTML · CSS · JavaScript · React · Three.js · Node.js · Python · PostgreSQL · SQL
🌐 HTML5 — Complete Reference
Document Structure
<!DOCTYPE html> — tells browser: HTML5 standard mode
<html lang="en"> — root element, lang for accessibility
<head> — metadata, not rendered; holds title, meta, links
<meta charset="UTF-8"> — character encoding
<meta name="viewport"> — responsive scaling on mobile
<title> — browser tab + SEO title (50-60 chars ideal)
<link rel="stylesheet"> — external CSS link
<script defer src> — JS load after DOM parse

Semantic Layout Tags
<header> — top of page or section header
<nav> — navigation links block
<main> — primary content, one per page
<section> — thematic grouping with heading
<article> — self-contained content (blog post, card)
<aside> — tangentially related content, sidebar
<footer> — bottom of page or section
<figure> + <figcaption> — image with caption
<details> + <summary> — native accordion
<dialog> — native modal dialog element
Text & Inline Elements
<h1>-<h6> — heading hierarchy, h1 once per page
<p> — paragraph block
<strong> — semantic bold (important)
<em> — semantic italic (emphasis)
<span> — inline container, no semantic meaning
<code> — inline code snippet
<pre> — preformatted text, preserves whitespace
<blockquote> — extended quotation with cite
<abbr title=""> — abbreviation with tooltip
<time datetime=""> — machine-readable time

Forms & Inputs
<form action method> — GET vs POST, action URL
<input type="text|email|password|number|date|file|checkbox|radio">
<label for=""> — links label to input via id
<textarea rows cols> — multiline text input
<select><option> — dropdown menu
<button type="submit|reset|button">
required, placeholder, min, max, pattern, autocomplete attributes
<fieldset><legend> — group related inputs
• HTML5 validation: built-in before JS runs
Media & Embeds
<img src alt loading="lazy"> — lazy load offscreen images
<picture><source srcset> — responsive images by breakpoint
<video controls autoplay muted loop> — HTML5 video
<audio controls src> — HTML5 audio player
<canvas> — 2D/3D drawing API (used by Three.js)
<svg> — inline vector graphics, scalable icons
<iframe src sandbox> — embed external content safely

Tables
<table><thead><tbody><tfoot> structure
<tr> — row, <th scope> — header cell, <td> — data cell
colspan rowspan — span multiple columns/rows
• Tables are for data only — never for layout

HTML5 APIs
• LocalStorage / SessionStorage — client-side key-value store
• Fetch API — modern AJAX, returns Promises
• Geolocation API — navigator.geolocation.getCurrentPosition
• Intersection Observer — lazy load, infinite scroll, animations
• ResizeObserver — react to element size changes
• Web Workers — run JS in background thread
• WebSocket API — full-duplex real-time connection
• Drag and Drop API — draggable elements natively
• History API — pushState/replaceState for SPA routing
🎨 CSS3 — Complete Reference
Selectors & Specificity
• Type: div (0,0,1) | Class: .box (0,1,0) | ID: #app (1,0,0)
• Universal: * | Descendant: div p | Child: div > p
• Adjacent: h1 + p | Sibling: h1 ~ p
• Attribute: [href^="https"] starts-with, [src$=".png"] ends-with
• Pseudo-class: :hover :focus :active :first-child :nth-child(2n+1) :not()
• Pseudo-element: ::before ::after ::placeholder ::selection ::first-line
• Specificity: inline(1000) > ID(100) > class(10) > tag(1)
!important overrides all — avoid it, use specificity instead

Box Model
• content → padding → border → margin (outside-in)
box-sizing: border-box — padding+border inside width
box-sizing: content-box — default, padding adds to width
margin: auto — horizontally centers block elements
• Margin collapse: vertical margins of adjacent blocks merge
outline — like border but outside box model, no layout impact

Display & Positioning
display: block | inline | inline-block | none | flex | grid | contents
position: static | relative | absolute | fixed | sticky
relative — offset from normal position, still in flow
absolute — removed from flow, relative to nearest positioned parent
fixed — relative to viewport, stays on scroll
sticky — relative until threshold, then fixed
z-index — stacking order (only works on positioned elements)
overflow: visible | hidden | scroll | auto | clip
Flexbox — Complete
display: flex — activates flex on container
flex-direction: row | column | row-reverse | column-reverse
justify-content: flex-start | center | flex-end | space-between | space-around | space-evenly
align-items: stretch | flex-start | center | flex-end | baseline
flex-wrap: nowrap | wrap | wrap-reverse
gap: 16px — spacing between flex items
flex-grow: 1 — item takes available space
flex-shrink: 0 — prevent item from shrinking
flex-basis: 200px — initial size before grow/shrink
flex: 1 1 auto — shorthand (grow shrink basis)
align-self — override align-items for one item
order: 2 — reorder items without changing HTML

CSS Grid — Complete
display: grid — activates grid on container
grid-template-columns: 1fr 2fr 1fr — 3-column layout
grid-template-columns: repeat(3, 1fr) — 3 equal columns
grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)) — responsive
grid-template-rows: 80px auto 60px — header/main/footer
gap: 16px 24px — row-gap column-gap
grid-column: 1 / 3 — span from col 1 to 3
grid-row: 1 / span 2 — span 2 rows from row 1
grid-area: header — named area placement
grid-template-areas — ASCII art layout mapping
justify-items | align-items — align inside cells
place-items: center — shorthand for both axes
Typography & Colors
font-family: 'Inter', sans-serif — always have fallback
font-size: 16px | 1rem | 1.2em — rem relative to :root
font-weight: 100-900 — thin to black
line-height: 1.5 — unitless, relative to font-size
letter-spacing: 0.05em — tracking
text-transform: uppercase | lowercase | capitalize
text-overflow: ellipsis — truncate with ... (needs overflow:hidden + white-space:nowrap)
color: #fff | rgb() | hsl() | oklch()
oklch() — perceptually uniform, best for color manipulation
background: linear-gradient(135deg, #f00, #00f)
background: radial-gradient(circle, #f00, transparent)

Animations & Transitions
transition: all 0.3s ease — smooth property changes
transition: transform 0.2s cubic-bezier(0.34,1.56,0.64,1) — spring feel
@keyframes slideIn { from{} to{} } — define animation
animation: slideIn 0.5s ease forwards — apply animation
animation-delay: 0.2s — stagger with delay
animation-iteration-count: infinite — loop forever
transform: translate() rotate() scale() skew()
• GPU-accelerated: only transform and opacity — avoid animating layout props

CSS Variables & Modern CSS
:root { --color-primary: #3b82f6; } — declare global variable
color: var(--color-primary, #000); — use with fallback
@media (max-width: 768px) — mobile breakpoint
@media (prefers-color-scheme: dark) — system dark mode
@media (prefers-reduced-motion: reduce) — accessibility
clamp(1rem, 2.5vw, 2rem) — fluid responsive typography
:is() :where() :has() — modern selector helpers
@layer — cascade layers for CSS architecture
@container — container queries for component-level responsive
⚡ JavaScript — Complete Deep Dive
Core Language
var — function-scoped, hoisted, avoid in modern JS
let — block-scoped, hoisted but in TDZ (Temporal Dead Zone)
const — block-scoped, cannot reassign (object props still mutable)
• Primitive types: string number boolean null undefined symbol bigint
typeof null === 'object' — famous JS bug, be aware
== coercion vs === strict equality — always use ===
• Truthy: everything except 0 "" null undefined NaN false
?? nullish coalescing — only null/undefined, not falsy
?. optional chaining — stops at null/undefined safely
• Destructuring: const {a, b} = obj | const [x, y] = arr
• Spread: {...obj} shallow clone | Rest: (...args) collect rest
• Template literals: `Hello ${name}` — tagged templates too

Functions
• Function declaration — hoisted fully, callable before declaration
• Function expression — not hoisted
• Arrow function: (x) => x * 2 — no own this, no arguments object
• Default params: function fn(x = 10)
• Closures: function retains reference to outer scope even after outer returns
• IIFE: (function() {})() — immediately invoked, creates private scope
• Currying: f(a)(b)(c) — partial application pattern
• Memoization: cache results of pure functions with Map
Async JavaScript
• Callbacks — first async pattern, leads to callback hell
• Promises: new Promise((resolve, reject) => {})
.then() — chainable, returns new Promise
.catch() — handle rejections
.finally() — always runs regardless
Promise.all([]) — parallel, fails fast on any rejection
Promise.allSettled([]) — waits all, gets success/fail per item
Promise.race([]) — first to settle wins
Promise.any([]) — first to fulfill wins
async/await — syntactic sugar, code reads synchronously
try/catch around await — handles promise rejection
• Event Loop: call stack → microtask queue (Promises) → macrotask queue (setTimeout)
• Microtasks run before next macrotask — critical ordering knowledge

Arrays — All Methods
.map(fn) — transform each element, returns new array
.filter(fn) — keep elements where fn returns true
.reduce(fn, init) — accumulate to single value
.forEach(fn) — iterate, returns undefined
.find(fn) — first matching element or undefined
.findIndex(fn) — index of first match or -1
.some(fn) — true if any element passes
.every(fn) — true if all elements pass
.flat(depth) — flatten nested arrays
.flatMap(fn) — map then flat one level
.includes(val) — check if value exists
.sort((a,b) => a-b) — sorts in place, ascending
.splice(start, count, ...items) — mutate in-place
.slice(start, end) — copy portion, non-mutating
Array.from() — convert iterables to arrays
Objects & Prototypes
• Object literal: { key: value, method() {} }
• Computed keys: { [varName]: value }
• Shorthand: { name, age } when var name matches key
Object.keys() .values() .entries() — iterate object
Object.assign({}, obj) — shallow merge/clone
Object.freeze(obj) — make immutable
• Prototype chain: every object has __proto__ link
class syntax — syntactic sugar over prototype inheritance
extends — subclass, super() — call parent constructor
static — method on class, not instance
get/set — computed properties, intercept access
• Private fields: #field — truly private since ES2022

DOM & Events
document.querySelector('.btn') — first match
document.querySelectorAll('li') — NodeList of all
element.addEventListener('click', handler)
• Event object: e.target e.currentTarget e.preventDefault() e.stopPropagation()
• Event bubbling: child → parent → document
• Event delegation: listen on parent, check e.target
element.innerHTML — parse HTML (XSS risk!)
element.textContent — plain text, safe from XSS
element.classList.add/remove/toggle/contains
element.setAttribute() getAttribute()
element.style.property = value — inline styles
IntersectionObserver — detect when element enters viewport

Modules & Tooling
export default — one per file, import as any name
export const — named, import with same name
import { fn } from './utils.js'
import * as utils from './utils.js'
• Dynamic import: const mod = await import('./heavy.js')
• Vite / Webpack — bundlers, tree-shaking removes unused code
• Babel — transpile modern JS to older browser targets
• ESLint + Prettier — linting and formatting in CI/CD
🐍 Python — Complete Reference
Core Language
• Dynamic typing — type inferred at runtime, use type hints for clarity
• Indentation-based scoping — 4 spaces standard (PEP 8)
• Everything is an object — even functions, classes, modules
None — Python's null, always compare with is None
is — identity check (same object in memory)
== — equality check (same value)
• String: immutable, f"Hello {name!r}" f-strings
str.split() join() strip() replace() startswith() endswith()
len() type() id() dir() help() — built-ins to know
range(start, stop, step) — lazy range object
• Unpacking: a, b, *rest = [1, 2, 3, 4, 5]
• Walrus operator: if (n := len(data)) > 10:

Data Structures
• List: [1,2,3] — ordered, mutable, O(1) append/index
• Tuple: (1,2,3) — ordered, immutable, faster than list
• Dict: {'key': val} — hash map, ordered since 3.7
• Set: {1,2,3} — unique elements, O(1) lookup
collections.defaultdict — auto-create missing keys
collections.Counter — count frequencies, .most_common()
collections.deque — O(1) append/popleft (use for BFS)
heapq — min-heap: heappush, heappop, heapify
• Negative heap trick: push -val to simulate max-heap
bisect — binary search on sorted lists
Comprehensions & Functional
• List comp: [x*2 for x in nums if x > 0]
• Dict comp: {k: v for k,v in items.items()}
• Set comp: {x**2 for x in range(10)}
• Generator expr: (x for x in huge_list) — lazy, memory efficient
map(fn, iterable) — apply function to each item
filter(fn, iterable) — keep items where fn is True
zip(a, b) — pair up iterables element by element
enumerate(lst, start=1) — index + value pairs
sorted(lst, key=lambda x: x[1], reverse=True)
lambda x: x*2 — anonymous function
functools.reduce(fn, iterable, init)
functools.lru_cache(maxsize=None) — memoization decorator

OOP & Classes
class Dog: — no explicit extends, implicit object
__init__(self, name) — constructor
self — explicit instance reference (not keyword, convention)
__str__ — str(obj), __repr__ — repr(obj), dev-friendly
__len__ __getitem__ __contains__ — dunder methods
@property — computed attribute, getter/setter
@classmethod — receives cls, factory methods
@staticmethod — no self/cls, utility method
• Inheritance: class Cat(Animal), super().__init__()
@dataclass — auto-generate __init__, __repr__, __eq__
• ABC: from abc import ABC, abstractmethod
Generators & Iterators
yield — turns function into generator, lazy execution
next(gen) — advance generator one step
yield from — delegate to sub-generator
__iter__ __next__ — make any object iterable
• Generator saves memory vs list for large data streams

Async Python
async def — coroutine function
await — yield control until awaitable resolves
asyncio.run(main()) — entry point
asyncio.gather(*coros) — run concurrently
asyncio.create_task(coro) — schedule coroutine
aiohttp — async HTTP client/server
• GIL (Global Interpreter Lock) — only one Python thread runs at a time
• Use threading for I/O-bound, multiprocessing for CPU-bound

Key Libraries
requests — HTTP client, simple and intuitive
FastAPI — async web framework, auto OpenAPI docs
SQLAlchemy — ORM, Core and ORM APIs
Pydantic — data validation with type hints
pytest — testing framework, fixtures, parametrize
numpy — arrays, vectorized math, broadcasting
pandas — DataFrames, groupby, merge, time series
black isort flake8 mypy — formatting, linting, type checking
• Virtual environments: python -m venv .venv, activate with source
🟢 Node.js — Complete Reference
Runtime & Architecture
• V8 Engine — compiles JS to machine code
• libuv — async I/O, event loop, thread pool
• Single-threaded event loop — non-blocking by design
• Thread pool (4 threads default) — handles file I/O, DNS, crypto
process.env — access environment variables
process.argv — CLI arguments array
process.exit(0) — exit with code (0 = success)
__dirname __filename — current dir/file paths
require() — CommonJS import (caches after first load)
module.exports = {} — CommonJS export
import/export — ES Modules with "type":"module" in package.json

Core Modules
fs — file system: readFile, writeFile, readdir, mkdir
fs.promises — async/await versions of all fs methods
path — path.join(), path.resolve(), path.extname()
http — createServer(), IncomingMessage, ServerResponse
https — TLS version of http module
crypto — createHash, createHmac, randomBytes, pbkdf2
os — platform, arch, cpus, totalmem, homedir
events — EventEmitter: on, emit, once, removeListener
stream — Readable, Writable, Transform, pipe()
buffer — binary data, Buffer.from(), buf.toString('hex')
child_process — exec, spawn, fork sub-processes
Express.js — Full Guide
const app = express() — create app instance
app.get('/path', (req, res) => {}) — route handler
app.post() app.put() app.patch() app.delete()
app.use('/api', router) — mount sub-router
req.params — URL params /user/:id
req.query — query string ?name=john
req.body — POST body (needs express.json() middleware)
req.headers — all request headers
res.json(data) — respond with JSON + Content-Type
res.status(404).json({error}) — status + body
res.redirect('/new-path') — HTTP redirect
res.sendFile(path) — serve static file
• Middleware chain: app.use((req, res, next) => { next() })
• Error middleware: (err, req, res, next) — 4 params
cors() — enable Cross-Origin Resource Sharing
helmet() — security headers (XSS, CSRF protection)
morgan — HTTP request logging
express-rate-limit — throttle requests per IP
multer — multipart/form-data file uploads
compression() — gzip responses
Authentication & Security
• JWT: jsonwebtoken.sign(payload, secret, {expiresIn})
• JWT: jsonwebtoken.verify(token, secret) — throws on invalid
• Bcrypt: bcrypt.hash(password, 12) — salt rounds = cost factor
• Bcrypt: bcrypt.compare(plain, hash) — returns boolean
• Never log passwords, tokens, or sensitive headers
• Store JWT secret in .env, never in code
• Cookie options: httpOnly: true, secure: true, sameSite: 'Strict'

Performance & Production
cluster module — fork workers to use all CPU cores
• PM2 — process manager: restart on crash, cluster mode, logs
• Streams for large files — never load entire file into memory
• Connection pooling for database — pg-pool, mongoose pooling
node --inspect — Chrome DevTools profiling
0/0 — handle uncaught exceptions + unhandled rejections
process.on('uncaughtException', handler)
process.on('unhandledRejection', handler)

npm & Package Management
npm init -y — create package.json
npm install pkg — add to dependencies
npm install -D pkg — add to devDependencies
package-lock.json — exact versions, commit this
npm ci — clean install from lockfile (use in CI/CD)
npm run script — run scripts from package.json
npx pkg — run package without installing globally
• Semantic versioning: ^1.2.3 minor OK, ~1.2.3 patch only
🎮 Three.js — 3D Web Graphics
Core Architecture
• Three.js wraps WebGL — no manual shader coding for basics
• Renderer → Scene → Camera → Objects pipeline
THREE.WebGLRenderer({canvas, antialias})
renderer.setSize(width, height)
renderer.setPixelRatio(window.devicePixelRatio) — crisp on retina
renderer.render(scene, camera) — draw one frame
requestAnimationFrame(animate) — game loop ~60fps

Scene & Camera
new THREE.Scene() — root container of all objects
scene.background = new THREE.Color(0x000000)
scene.fog = new THREE.Fog(color, near, far)
PerspectiveCamera(fov, aspect, near, far) — human-like view
fov: field of view in degrees (75 is natural)
aspect: window.innerWidth / window.innerHeight
OrthographicCamera — no perspective, for UI/2D
camera.position.set(x, y, z) — place camera
camera.lookAt(target) — point at object
Geometry & Materials
BoxGeometry(w, h, d) — cube with segments
SphereGeometry(r, widthSeg, heightSeg)
PlaneGeometry(w, h) — flat surface
CylinderGeometry(rTop, rBot, h, seg)
TorusGeometry(r, tube, radSeg, tubeSeg) — donut
BufferGeometry — raw vertex data, max performance
MeshBasicMaterial — unlit, always full brightness
MeshStandardMaterial — PBR physically-based, needs lights
MeshPhongMaterial — shininess, cheaper than PBR
• Material props: color wireframe transparent opacity side
new THREE.Mesh(geometry, material) — combine to renderable
scene.add(mesh) — add to scene

Lights
AmbientLight(color, intensity) — all-direction flat light
DirectionalLight(color, intensity) — sun-like parallel rays
PointLight(color, intensity, distance) — light bulb
SpotLight — cone-shaped beam with shadows
light.castShadow = true — enable shadow casting
renderer.shadowMap.enabled = true
Textures & Loading
TextureLoader().load('img.jpg') — load image as texture
material.map = texture — apply color texture
material.normalMap — surface bumps
material.roughnessMap material.metalnessMap — PBR maps
GLTFLoader — load .gltf/.glb 3D models
loader.load(url, (gltf) => scene.add(gltf.scene))
LoadingManager — track multiple asset loads

Animation & Interaction
mesh.rotation.y += 0.01 — rotate in animate loop
mesh.position.x = Math.sin(clock.getElapsedTime())
THREE.Clock — delta time for frame-rate independent animation
AnimationMixer — play animations from GLTF models
Raycaster — mouse click → 3D object picking
raycaster.setFromCamera(mouse, camera)
raycaster.intersectObjects(scene.children)
• OrbitControls — mouse drag to rotate/zoom/pan camera
• GSAP — smooth animation library, pairs perfectly with Three.js
renderer.domElement — canvas to append to document
🐘 SQL & PostgreSQL — Complete Reference
SQL Fundamentals
• DDL (Data Definition): CREATE TABLE ALTER TABLE DROP TABLE TRUNCATE
• DML (Data Manipulation): SELECT INSERT UPDATE DELETE
• DCL (Data Control): GRANT REVOKE
• TCL (Transaction Control): BEGIN COMMIT ROLLBACK SAVEPOINT

SELECT — Full Syntax
SELECT col1, col2 FROM table — basic query
SELECT DISTINCT col — unique values only
WHERE col = 'val' AND age > 18 — filter rows
WHERE col IN (1,2,3) — match any in list
WHERE col BETWEEN 10 AND 20 — inclusive range
WHERE name LIKE 'J%' — % wildcard, _ single char
WHERE email IS NULL / IS NOT NULL
ORDER BY col ASC | DESC, col2 ASC
LIMIT 10 OFFSET 20 — pagination
GROUP BY col HAVING COUNT(*) > 5
• Execution order: FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY → LIMIT

JOINs — All Types
INNER JOIN — only matching rows in both tables
LEFT JOIN — all left rows + matching right (NULL if no match)
RIGHT JOIN — all right rows + matching left
FULL OUTER JOIN — all rows from both, NULL where no match
CROSS JOIN — cartesian product, every row × every row
SELF JOIN — join table to itself (manager/employee)
• Join on: ON a.id = b.user_id
• Multiple joins: chain them — FROM a JOIN b ON ... JOIN c ON ...
Aggregate Functions
COUNT(*) — all rows, COUNT(col) — non-NULL only
SUM(col) AVG(col) MIN(col) MAX(col)
STRING_AGG(col, ',') ARRAY_AGG(col) — PostgreSQL
GROUP_CONCAT(col) — MySQL equivalent

Window Functions (Advanced)
ROW_NUMBER() OVER (ORDER BY salary DESC) — unique rank
RANK() — ties get same rank, next rank skipped
DENSE_RANK() — ties same rank, no skip
NTILE(4) OVER (...) — divide into quartiles
LAG(col, 1) OVER (ORDER BY date) — previous row value
LEAD(col, 1) OVER (ORDER BY date) — next row value
SUM(col) OVER (PARTITION BY dept ORDER BY date) — running total
FIRST_VALUE(col) OVER (...) — first in window
PARTITION BY — reset window per group

CTEs & Subqueries
• CTE: WITH cte AS (SELECT ...) SELECT * FROM cte
• Multiple CTEs: WITH a AS (...), b AS (...) SELECT ...
• Recursive CTE: WITH RECURSIVE tree AS (...) — for hierarchies
• Subquery in WHERE: WHERE id IN (SELECT user_id FROM orders)
• Correlated subquery: references outer query — runs per row
EXISTS (SELECT 1 FROM ...) — faster than IN for large sets
• Scalar subquery: SELECT (SELECT MAX(salary) FROM emp)
PostgreSQL-Specific
SERIAL or BIGSERIAL — auto-increment integer
UUID type + gen_random_uuid() function
JSONB — binary JSON, indexable, faster queries
ARRAY type — store arrays natively in columns
ENUMCREATE TYPE mood AS ENUM ('happy','sad')
• Full-text search: tsvector tsquery to_tsvector to_tsquery
pg_trgm extension — trigram similarity for fuzzy search
EXPLAIN ANALYZE — show query plan + actual timing
VACUUM ANALYZE — reclaim dead tuples, update stats
• Partitioning: RANGE, LIST, HASH partitioning for huge tables
LISTEN/NOTIFY — pub/sub between DB sessions

Indexes & Performance
• B-Tree index (default) — equality + range queries
• Hash index — equality only, faster than B-Tree for =
• GIN index — for JSONB, arrays, full-text search
• GiST index — geometric data, full-text, range types
• Partial index: CREATE INDEX ON users(email) WHERE active = true
• Composite index: column order matters — put = cols first
• Covering index: INCLUDE (col3, col4) — avoid table lookup
• Index on expression: CREATE INDEX ON users(lower(email))
• Too many indexes slow writes — balance read vs write ratio

Transactions & Locking
BEGIN; ... COMMIT; or ROLLBACK;
• Isolation: READ COMMITTED (default) → REPEATABLE READ → SERIALIZABLE
• Row-level locks: SELECT ... FOR UPDATE
• Advisory locks: pg_advisory_lock(id) — application-level
• Deadlock detection — PostgreSQL auto-detects and aborts one tx
• MVCC (Multi-Version Concurrency Control) — readers don't block writers
⚛️ React — Deep Dive
Hooks Reference
useState — local state, re-renders on change
useEffect(fn, deps) — side effects: API calls, subscriptions
useContext(Ctx) — read context value
useReducer(reducer, init) — complex state logic
useRef(val) — mutable ref, DOM access, no re-render
useMemo(() => calc, deps) — memoize expensive value
useCallback(fn, deps) — memoize function reference
useLayoutEffect — synchronous, after DOM paint
useId — stable unique ID for SSR
useTransition — mark state update as non-urgent
useDeferredValue — defer re-render for stale UI

Performance
React.memo(Component) — skip re-render if props unchanged
• Keys in lists — stable keys prevent unnecessary DOM updates
• Code splitting: React.lazy(() => import('./Component'))
Suspense fallback — show loading while lazy loads
🔷 TypeScript — Must Know
Type System
• Primitive types: string number boolean null undefined void never
type vs interface — interface is extendable, type for unions
• Union: string | number — one of these types
• Intersection: TypeA & TypeB — must satisfy both
• Generic: function identity<T>(val: T): T
• Utility types: Partial<T> Required<T> Readonly<T> Pick<T,K> Omit<T,K>
Record<K,V> — object with specific key/value types
• Type narrowing: typeof instanceof in guards
as const — literal types, prevent widening
keyof T — union of keys of T
typeof obj — infer type from value
• Mapped types: { [K in keyof T]: T[K] }
• Conditional types: T extends U ? X : Y
🔴 Git — Advanced Commands
Daily Commands
git stash / git stash pop — save work temporarily
git cherry-pick <hash> — apply specific commit
git rebase -i HEAD~3 — interactive rebase, squash commits
git reset --soft HEAD~1 — undo commit, keep changes staged
git reset --hard HEAD~1 — undo commit, lose changes
git reflog — find lost commits
git bisect — binary search for bug-introducing commit
git blame file.js — who changed each line and when
git log --oneline --graph --all — visual branch history
git tag v1.0.0 -m "Release" — annotated release tag
git submodule — embed repos within repos
.gitignore — patterns: node_modules/ .env *.log dist/
🧪 Testing — Full Stack
Testing Pyramid
• Unit tests (70%) — test single function in isolation
• Integration tests (20%) — test combined modules
• E2E tests (10%) — simulate real user flows

JavaScript Testing
• Jest: describe() it() expect() beforeEach() afterEach()
jest.mock('./module') — mock dependencies
jest.spyOn(obj, 'method') — spy + stub
• React Testing Library: test behavior not implementation
render() screen.getByText() userEvent.click()
• Vitest — faster Jest alternative for Vite projects
• Playwright / Cypress — E2E browser automation

Python Testing
pytest — functions starting with test_
@pytest.fixture — reusable setup/teardown
@pytest.mark.parametrize — test multiple inputs
unittest.mock.patch — mock external dependencies
Leadership & Product Sense
Soft skills for Staff Engineers and beyond.
Leading Engineers
• **Mentorship**: Sponsoring vs Coaching
• **Design Reviews**: Critical feedback loops
• **Conflict resolution**: Tech-drift management
Product Intelligence
• **North Star Metrics**: Defining success
• **Prioritization**: RICE & Eisenhower methods
• **Trade-off Analysis**: Time-to-market vs Quality
Staff Tip: The RFC Process
Always lead with a written proposal before coding a major system.
Company Intelligence
Insider tracks on FAANG review processes.
Google
Focus: Complexity & Googliness.
• Deep dive into Algorithms logic
• "Googliness" behavioral signals
• System Design: Scale & Latency focus
Meta
Focus: Speed & Product Sense.
• 2-3 Mediums in 45 mins
• Product architecture interview
• Cultural alignment with "Move Fast"
Amazon
Focus: Leadership Principles.
• LP questions in EVERY round
• Bar Raiser interview rounds
• Coding + Object Oriented Design
Apple
Focus: Hardware-Software & Privacy.
• Deep OS/Hardware internals
• Cross-team behavioral rounds
• Security & Privacy focus in design
LLD & Design Patterns
Object-oriented mastery and code modularity.
Creational Patterns
• **Singleton**: Unique instance management
• **Factory**: Interface-based instantiation
• **Builder**: Complex object construction
Structural Patterns
• **Adapter**: Bridging incompatible interfaces
• **Decorator**: Adding dynamic responsibilities
• **Proxy**: Placeholder for access control
Behavioral Patterns
• **Observer**: Subscription mechanisms
• **Strategy**: Swappable logic algorithms
• **Command**: Encapsulating actions as objects
SOLID Principles
S-O-L-I-D Framework
Single Resp · Open/Closed · Liskov Sub · Interface Seg · Dependency Inversion
The Project Lab
High-impact engineering blueprints for your portfolio.
Tier 1: Distributed Messenger
Fullstack Real-time Communication
• **Tech**: WebSockets, Redis, PostgreSQL, React
• **Challenge**: Handling million concurrent connections
• **Signal**: Demonstrates concurrency and low-latency design.
Tier 2: Cloud Sandbox OS
Web-based Terminal Interface
• **Tech**: XTerm.js, Docker, WebAssembly, Go
• **Challenge**: Secure container execution in browser
• **Signal**: Demonstrates security and systems knowledge.
Tier 3: AI Market Predictor
TimeSeries Forecasting with LLM Signals
• **Tech**: Python, PyTorch, News API, RAG
• **Challenge**: Sentiment-driven volume prediction
• **Signal**: Demonstrates ML and data engineering maturity.
Portfolio Matrix
Focus on projects that showcase **Scalability**, **Security**, and **Algorithm Optimization**.
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