Walmart SDE-3 Interview Experience (1.10 YOE | DSA + LLD + HLD)

Hi everyone,

I recently attended the Walmart SDE-3 interview process. I currently have 1 year 10 months of experience at a fintech startup.

Here’s a detailed breakdown of the rounds:

🔹 Round 1 – DSA (Graphs)

Question 1: Number of Islands
Follow-up: Modify the solution to count unique island shapes

Focus Areas:

• DFS / BFS traversal
• Grid traversal patterns
• Connected components
• Encoding island shapes (relative positioning technique)
• Time & space complexity discussion

Difficulty: Medium → Medium-Hard (because of the follow-up)

🔹 Round 2 – LLD (Java)

Design a ThreadPoolExecutor (similar to Java’s internal implementation)

Asked to cover:

• Class diagram
• Relationships between classes
• Important variables and methods
• Internal data structures
• Thread lifecycle management
• Task submission and execution flow
• Concurrency handling and synchronization
• Rejection policies

Key Components Discussed:

• Worker class
• BlockingQueue for task storage
• Runnable tasks
• Core pool size vs Maximum pool size
• Keep-alive time
• Thread reuse
• Graceful shutdown

Concepts Tested:

• Java concurrency
• Object-oriented design
• SOLID principles & Design patterns explanation with examples
• Race conditions & synchronization strategies

This round was deep and required strong understanding of internal working, not just surface-level usage.

🔹 Round 3 – HLD

Design an Online Chess Game System

Functional Requirements:

• Users can create and join matches
• Real-time gameplay
• Ranking system for each user
• Leaderboard updates in near real-time
• Two types of ranking:
  • Global Rank
  • Local Rank

High-Level Design Discussion:

• WebSockets for real-time move updates
• Matchmaking service
• Game service to maintain board state
• Persistent storage for matches and user stats
• Ranking calculation (ELO-based approach)
• Leaderboard service (Redis Sorted Sets for fast rank computation)
• Scalability considerations
• Handling concurrent games
• Low-latency updates

Concepts Tested:

• Distributed systems
• Real-time architecture
• Caching strategies
• Horizontal scalability
• Consistency vs availability trade-offs

3rd went pretty well until last 10 mins, in last 10 mins I over engineered and made design complex for scaling - so as expected I got negative feedback for this round and got rejected.

Overall Experience

The process was very well-rounded and tested:

• ✅ Strong DSA fundamentals
• ✅ Deep concurrency & LLD knowledge
• ✅ Real-time system design and scalability thinking

It was a great learning experience.