CS Core

"Master the fundamentals, and the rest will follow."

This section covers the foundational computer science knowledge that every backend engineer should master. These concepts form the bedrock of all software systems and demonstrate a deep understanding beyond just API integrations.

Why CS Fundamentals Matter

In technical interviews and real-world engineering, understanding why things work is just as important as knowing how to use them.

Real-world impact:

• Poor algorithm choice: O(n²) vs O(n log n) can mean seconds vs hours of processing
• Missing database index: Query takes 10 seconds instead of 10 milliseconds
• Not understanding TCP: Can't debug connection issues or optimize performance
• Weak system design: System crashes under load that could have been handled

Topics Covered

Algorithms & Data Structures

Systematic problem-solving patterns and efficient data organization.

What you'll learn:

• Algorithm patterns (Two Pointers, Sliding Window, Dynamic Programming)
• Core data structures (Arrays, Linked Lists, Trees, Graphs, Hash Tables)
• Time & Space complexity analysis (Big O notation)

Why it matters:

• Write efficient code that scales
• Solve coding interview problems confidently
• Choose the right data structure for the job

System Design

Building scalable, reliable, and maintainable systems.

What you'll learn:

• High concurrency & availability patterns
• Distributed systems fundamentals (CAP theorem, BASE)
• Load balancing, caching, and message queues
• Real-world system architecture (e.g., URL shortener, notification system)

Why it matters:

• Design systems that handle millions of users
• Make trade-offs between consistency, availability, and partition tolerance
• Senior+ engineers are expected to design complex systems

Database

Deep dive into MySQL and Redis internals.

What you'll learn:

• MySQL: Architecture, indexes (B+ Tree), transactions (ACID), locking, replication
• Redis: Data structures, caching patterns, persistence, clustering

Why it matters:

• Database is often the bottleneck in web applications
• Understanding indexes prevents 1000x performance differences
• Transactions and isolation levels prevent data corruption
• Proper caching reduces database load by 90%

Network & OS

The infrastructure that powers everything.

What you'll learn:

• TCP/IP handshake, HTTP/HTTPS protocols
• Linux essentials, process management, shell scripting
• Memory management, file systems, concurrency

Why it matters:

• Debug connection issues and network problems
• Understand how your application interacts with the OS
• Optimize performance through system calls and I/O

Learning Path

For Interview Preparation

1-3 months before interview:

1. Algorithms (4-6 weeks)

   • Practice 2-3 LeetCode problems daily
   • Focus on patterns, not individual problems
   • Master: Arrays, Strings, Linked Lists, Trees, Hash Tables, Graphs

2. System Design (2-3 weeks)

   • Learn design patterns (load balancing, caching, sharding)
   • Practice designing 3-5 systems end-to-end
   • Understand trade-offs (consistency vs availability)

3. Database & Network (1-2 weeks)

   • Review MySQL indexes and transactions
   • Understand Redis caching strategies
   • Review TCP/IP and HTTP basics

For Professional Growth

Ongoing learning:

1. Start with what you use daily

   • Backend engineer → Database, System Design
   • Infrastructure engineer → Network & OS, System Design
   • Full-stack → All topics progressively

2. Learn by doing

   • Optimize slow queries in your application
   • Design a new feature with scalability in mind
   • Debug network issues using Wireshark/tcpdump

3. Teach others

   • Explain concepts to teammates
   • Write blog posts or give talks
   • Teaching reinforces learning

Quick Reference

Topic	Key Concepts	Interview Focus	Time Investment
Algorithms	Sorting, Searching, Graph, DP	LeetCode Medium/Hard	4-6 weeks
System Design	Scalability, Reliability, CAP	Senior+ Interviews	2-4 weeks
Database	Indexing, Transactions, Caching	Backend Roles	2-3 weeks
Network/OS	TCP/IP, HTTP, Linux	Infrastructure Roles	1-2 weeks

Common Interview Questions by Topic

Algorithms

• Explain the time complexity of your solution
• How would you optimize this algorithm?
• Trade-offs between different data structures

System Design

• Design a URL shortener (like bit.ly)
• Design a rate limiter
• How would you scale Twitter's timeline?

Database

• Explain the difference between B+ Tree and Hash index
• How does MVCC work in MySQL?
• What's the difference between RC and RR isolation levels?

Network & OS

• What happens when you type a URL in the browser?
• Explain TCP three-way handshake
• How does HTTPS work?

Resources

Practice Platforms

• LeetCode: Algorithm practice
• Pramp: Mock interviews
• System Design Primer: GitHub repo for system design

Books

• "Introduction to Algorithms" (CLRS)
• "Designing Data-Intensive Applications" (Martin Kleppmann)
• "Computer Networking: A Top-Down Approach"

Documentation

• MySQL Official Documentation
• Redis Documentation
• Linux man pages

Next Steps

1. Choose your starting point based on your current role and interview timeline
2. Set a schedule - Consistent daily practice beats cramming
3. Track progress - Note which topics you've mastered and what needs work
4. Apply knowledge - Use these concepts in real projects

Dive into any topic:

• Algorithms & Data Structures - Start here for coding interviews
• System Design - Essential for senior roles
• Database - MySQL and Redis internals
• Network & OS - TCP/IP and Linux fundamentals