Stop blanking on coding questions

Data Structures & Algorithms

Arrays, trees, graphs, dynamic programming, sliding window, BFS/DFS — explained step by step with time/space complexity analysis.

"Find the longest substring without repeating characters"

Use a sliding window with a HashSet. Expand right pointer, shrink left when duplicate found. O(n) time, O(min(n,m)) space where m is charset size.

SQL & Database

Query optimization, JOINs, window functions, indexing strategies, normalization, stored procedures.

"This query scans 12M rows and takes 8 seconds — how would you optimize it?"

Add a composite index on (status, created_at). Rewrite the subquery as a JOIN to avoid correlated scan. Consider partitioning by date if this is a time-series access pattern.

System Design

End-to-end system architecture for distributed systems. Load balancing, caching, sharding, message queues, microservices.

"Design a URL shortener that handles 100M URLs"

Base62 encoding of auto-increment ID. Write to primary DB, async replicate to read replicas. Cache hot URLs in Redis with LRU eviction. 301 redirect for SEO. Rate limit by API key.

Object-Oriented Design

Class hierarchies, design patterns, SOLID principles, interface design. Common OOD interview questions answered with clean code.

"Design a parking lot system"

ParkingLot has multiple Levels, each has list of ParkingSpots (Small/Medium/Large). Vehicle abstract class with Car/Truck/Motorcycle subclasses. Strategy pattern for spot assignment. Observer pattern to notify when lot is full.

Python / JavaScript / Java

Language-specific questions — closures, event loop, GIL, memory management, async/await, generics, type systems.

"Explain the Node.js event loop and why it matters"

Single-threaded with non-blocking I/O. Call stack executes sync code. Libuv handles async ops (file I/O, network) in thread pool. Callbacks queued in event loop phases: timers → I/O → setImmediate → close. This is why a CPU-bound task blocks everything.

API Design & REST

RESTful conventions, GraphQL trade-offs, versioning, pagination, authentication, rate limiting.

"Design an API for a social media feed"

GET /feed?cursor=abc&limit=20 with cursor-based pagination. Fan-out-on-read for small user graphs, fan-out-on-write for celebrity follows. Cache timeline in Redis sorted set. ETag headers for conditional requests.