🧠 Core CS Concepts

📂 Topics Covered

🎯 Quick Reference

Time Complexity

| Notation | Name | Example | |———-|——|———| | O(1) | Constant | Array access | | O(log n) | Logarithmic | Binary search | | O(n) | Linear | Linear search | | O(n log n) | Linearithmic | Merge sort | | O(n²) | Quadratic | Bubble sort | | O(2ⁿ) | Exponential | Recursive Fibonacci |

Data Structures

• Array - Contiguous memory, O(1) access
• Linked List - Dynamic size, O(n) access
• Stack - LIFO (Last In First Out)
• Queue - FIFO (First In First Out)
• Hash Table - O(1) average lookup
• Tree - Hierarchical structure
• Graph - Nodes and edges

Authentication Flow

1. User Login → Server validates
2. Server → Access Token (short-lived) + Refresh Token (long-lived)
3. API Request → Access Token in header
4. Token Expired → Use Refresh Token to get new Access Token

📚 Resources

• Big-O Cheat Sheet
• Visualgo
• GeeksforGeeks

Last Updated: March 2026