🔥 Ultimate Coding Interview Cheat Sheet (2025 Edition)

✅ 1. Data Structures
Key Concepts:
• Arrays/Lists
• Strings
• Hashmaps (Dicts)
• Stacks & Queues
• Linked Lists
• Trees (BST, Binary)
• Graphs
• Heaps

Practice Questions:
• Reverse a string or array
• Detect duplicates in an array
• Find missing number
• Implement stack using queue
• Traverse binary tree (Inorder, Preorder)

✅ 2. Algorithms
Key Concepts:
• Sorting (Quick, Merge, Bubble)
• Searching (Binary search)
• Recursion
• Backtracking
• Divide & Conquer
• Greedy
• Dynamic Programming

Practice Questions:
• Fibonacci with DP
• Merge sort implementation
• N-Queens Problem
• Knapsack problem
• Coin change

✅ 3. Problem Solving Patterns
Important Patterns:
• Two Pointers
• Sliding Window
• Fast & Slow Pointer
• Recursion + Memoization
• Prefix Sum
• Binary Search on answer

Practice Questions:
• Longest Substring Without Repeat
• Max Sum Subarray of Size K
• Linked list cycle detection
• Peak Element

✅ 4. System Design Basics
Key Concepts:
• Scalability, Load Balancing
• Caching (Redis)
• Rate Limiting
• APIs and Databases
• CAP Theorem
• Consistency vs Availability

Practice Projects:
• Design URL shortener
• Design Twitter feed
• Design chat system (e.g., WhatsApp)

✅ 5. OOP & Programming Basics
Key Concepts:
• Classes & Objects
• Inheritance, Polymorphism
• Encapsulation, Abstraction
• SOLID Principles

Practice Projects:
• Design a Library System
• Implement Parking Lot
• Bank Account Simulation

✅ 6. SQL & Database Concepts
Key Concepts:
• Joins (INNER, LEFT, RIGHT)
• GROUP BY, HAVING
• Subqueries
• Window Functions
• Indexing

Practice Queries:
• Get top 3 salaries
• Find duplicate emails
• Most frequent orders per user

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