SDE 3 Prep Guide

Welcome to the SDE 3 / Senior Software Engineer Coding Preparation Guide. SDE 3 interviews focus on not just solving the problem, but solving it gracefully while handling edge cases, optimal data structures, and often introducing low-level system design or concurrency elements into the code.

1. Advanced Data Structures & Algorithms (DSA)

Unlike SDE 1/2 interviews, SDE 3 problems often combine topics. You might need to use a Segment Tree for a sliding window problem or a Trie for a graph traversal problem.

• Advanced DP Patterns

  • Digit DP, Bitmask DP, Tree DP

• Advanced Graphs

  • Strongly Connected Components (Tarjan), Articulation Points/Bridges.

• Tries & Segment Trees

  • String manipulation at scale, answering range queries.

2. Low-Level Design (LLD) Problem Integration

SDE 3 coding rounds often blur the line with Machine Coding / Object Oriented Design. You are expected to write code that is Extensible, Maintainable, and SOLID.

• Examples:

  • Design a Rate Limiter (Token Bucket / Leaky Bucket Implementation)

  • Design an In-Memory File System (Requires heavy use of Tries/Trees and HashMap OOP)

  • Design an LRU / LFU Cache (Combining HashMaps with Doubly Linked Lists)

• Key Focus: Use appropriate interfaces (abstract classes and protocols), encapsulate state, and use threading locks if required.

3. Concurrency and Multithreading

SDE 3 roles usually require backend or distributed systems expertise where concurrency knowledge is critical.

• Concurrency Patterns

  • Readers-Writers Lock, Producer-Consumer architecture using wait/notify logic.

  • Avoiding deadlocks and starvation strategies.

4. Top 20 Curated SDE 3 Focus Problems

Practice these specific archetypes:

1. Word Search II (Trie + Backtracking)

2. Alien Dictionary (Topological Sort Graph)

3. Serialize and Deserialize Binary Tree (Design + Tree Traversal)

4. LFU Cache (Advanced Data Structures + OOD)

5. Merge K Sorted Lists (Heaps / Priority Queue)

6. Median of Two Sorted Arrays (Advanced Binary Search)

7. Sliding Window Maximum (Monotonic Queue / Deque)

8. Trapping Rain Water (Two Pointers / Monotonic Stack)

9. Critical Connections in a Network (Tarjan's Bridge finding algorithm)

10. Regular Expression Matching (2D DP)

11. Burst Balloons (Matrix Chain Multiplication / Interval DP)

12. The Skyline Problem (Segment Tree / Balanced BST / Heap)

13. Find Median from Data Stream (Two Heaps)

14. Design Search Autocomplete System (Trie + Heap OOD)

15. Design Tic-Tac-Toe (O(1) checks per move)

16. Longest Valid Parentheses (DP or Stack)

17. Maximum XOR of Two Numbers in an Array (Binary Trie)

18. Print FooBar Alternately (Concurrency semantics)

19. Dining Philosophers (Concurrency / Deadlock avoidance)

20. Reconstruct Itinerary (Hierholzer's Algorithm / Eulerian Path)