Had an interesting and well-structured coding round with Paytm for a Technical Lead role. Sharing a quick summary that might help others preparing 👇

🧠 Round Focus

The interview was a mix of:

• Core DSA fundamentals
• Problem-solving approach
• Clean code + explanation
• Some discussion around real-world usage of problems

🔹 Question 1: LRU Cache

• Classic design problem (similar to LeetCode 146)

• Expected O(1) get and put

• Key focus areas:

  • Combining HashMap + Doubly Linked List
  • Handling edge cases like updates & eviction
  • Writing clean, modular code

👉 Follow-up discussion:

• Thread safety considerations
• Why not use LinkedHashMap directly
• Real-world use cases (caching, DB optimization)

🔹 Question 2: Course Schedule

• Graph-based problem (LeetCode 207)
• Detect if all courses can be completed

👉 Approach:

• Modeled as Directed Graph
• Solved using DFS cycle detection (Topological sort concept)

👉 Follow-ups:

• BFS (Kahn’s Algorithm) alternative
• How to return course order (Course Schedule II)
• Real-world analogy (task dependencies, job scheduling)

💬 Discussion Highlights

• Interviewer focused more on thought process than just code

• Asked about trade-offs, optimizations, and edge cases

• Some behavioral questions around:

  • Transition to Technical Lead
  • Ownership & system design thinking

🎯 Key Takeaways

• Be very clear with fundamentals (HashMap, Graphs, Linked List)

• Always explain:

  • Why this approach?
  • Time & Space complexity

• Think beyond code → real-world systems & scalability

• Communication matters as much as correctness

🚀 Final Tip

If you're targeting Paytm (or similar product companies), prepare:

• LRU Cache, LFU Cache
• Graph problems (cycle detection, topological sort)
• System design basics (caching, async processing, idempotency)

Happy to discuss more if anyone is preparing for similar roles 🙌