High-Level & Low-Level Design Interview Problems

What you'll learn

• Explain what high-level (HLD) and low-level (LLD) design rounds assess and run each with a compact, repeatable approach.
• Turn requirements into classes, relationships and interfaces, applying SOLID and a few patterns where they genuinely help.
• Solve classic LLD problems such as a parking lot, elevator, vending machine, seat booking, LRU cache and rate limiter.
• Design large systems such as ride-hailing, checkout, video streaming, key-value stores, autocomplete and payment ledgers.
• Reason about consistency, idempotency, partitioning, replication and failure modes with clearly stated assumptions.
• Present designs with clear diagrams, explicit trade-offs and a structured practice plan.

Syllabus

How Design Rounds Work

1. HLD Versus LLD Rounds
2. A Compact Approach for Each Round
3. Common Mistakes

LLD Fundamentals for Interviews

1. Finding Entities and Relationships
2. SOLID Applied Briefly
3. Patterns That Recur in LLD

LLD Problems I

1. Design a Parking Lot
2. Design an Elevator System
3. Design a Vending Machine

LLD Problems II

1. Seat Booking With Concurrency
2. Design an LRU Cache Class
3. Design a Rate Limiter Class

HLD Problems I

1. Design a Ride-Hailing Service
2. Design E-commerce Checkout and Inventory
3. Design a Video Streaming Platform

HLD Problems II

1. Design a Distributed Key-Value Store
2. Design Search Autocomplete
3. Design a Payment System and Ledger

HLD Problems III

1. Design Collaborative Document Editing
2. Design a Distributed Job Scheduler
3. Design a Metrics and Logging Pipeline

Delivering and Practising

1. Drawing Clear Diagrams
2. Discussing Trade-offs and Failure Modes
3. A Practice Plan and Problem List
4. Final Design Interview Checklist