Difference Between SDE-1, SDE-2, and SDE-3 Interview Levels Explained

SDE-2 Level Questions (Focus: Optimization and Design)

1. Find Duplicates in an Array (Amazon) Problem: Find duplicates with O(1) space. Solution: Modify array as visited marker (negate values). If already negative, duplicate. Restore if needed. Time: O(n). Why asked: Space optimization.
2. Multiply Strings (Microsoft) Problem: Multiply large numbers as strings. Solution: Simulate manual multiplication, handle carry. Use array for digits. Time: O(m*n). Why asked: Big integer handling.
3. Implement Atoi (Google) Problem: String to int. Solution: Handle signs, overflow (clamp to INT_MIN/MAX), ignore non-digits after start. Why asked: Edge cases like overflow.
4. Length of the Longest Substring Without Repeating Characters (Amazon) Problem: Find max unique substring length. Solution: Sliding window with set. Move left on duplicate. Time: O(n). Why asked: Window techniques.
5. Merge K Sorted Linked Lists (Microsoft) Problem: Merge k lists. Solution: Min-heap of list heads. Pop min, add next. Time: O(n log k). Why asked: Priority queues.
6. Add Two Numbers Represented by Linked Lists (Google) Problem: Add two numbers as lists. Solution: Traverse with carry, build new list. Handle unequal lengths. Time: O(max(m,n)). Why asked: List arithmetic.
7. Search an Element in a Sorted and Rotated Array (Amazon) Problem: Search in rotated sorted array. Solution: Binary search variant. Find pivot, search appropriate half. Time: O(log n). Why asked: Modified binary search.
8. Square Root of an Integer (Microsoft) Problem: Integer sqrt. Solution: Binary search from 1 to x/2. Time: O(log n). Why asked: Math optimization.
9. Sort an Array of 0s, 1s, and 2s (Google) Problem: Sort 0-1-2 array. Solution: Dutch National Flag: Low/mid/high pointers. Swap based on mid. Time: O(n). Why asked: Partitioning.
10. Check for Balanced Brackets in an Expression (Amazon) Problem: Validate brackets. Solution: Stack: Push open, pop on close if matches. Time: O(n). Why asked: Stack applications.

SDE-3 Level Questions (Focus: Scalability and Leadership)

1. Diameter of a Binary Tree (Amazon) Problem: Longest path in tree. Solution: DFS: For each node, max(left_height + right_height). Update global max. Time: O(n). Why asked: Tree recursion.
2. Lowest Common Ancestor in a Binary Tree (Microsoft) Problem: Find LCA. Solution: Recursive: If root is p/q, return root. Else recurse left/right, combine results. Time: O(n). Why asked: Tree traversal.
3. Serialize and Deserialize a Binary Tree (Google) Problem: Tree to string and back. Solution: Preorder traversal with markers for null. Deserialize with queue. Time: O(n). Why asked: Serialization.
4. Find the Number of Islands (Amazon) Problem: Count islands in grid. Solution: DFS/BFS on ‘1’s, mark visited. Count components. Time: O(m*n). Why asked: Graph connectivity.
5. Topological Sort (Microsoft) Problem: Topo sort DAG. Solution: Kahn’s algo: Indegree array, queue zeros, reduce indegrees. Time: O(V+E). Why asked: Dependency resolution.
6. K Largest Elements (Google) Problem: Find k largest. Solution: Min-heap of size k. Add if > root, replace. Time: O(n log k). Why asked: Heap usage.
7. 0-1 Knapsack Problem (Amazon) Problem: Max value with weight limit. Solution: DP table: dp[i][w] = max(dp[i-1][w], dp[i-1][w-weight[i]] + value[i]). Time: O(n*W). Why asked: Classic DP.
8. Longest Common Subsequence (Microsoft) Problem: LCS length. Solution: DP: If match, dp[i][j] = dp[i-1][j-1] + 1; else max(left, up). Time: O(m*n). Why asked: String DP.
9. N-Queen Problem (Google) Problem: Place n queens safely. Solution: Backtracking: Place row-by-row, check columns/diagonals. Time: O(n!). Why asked: Backtracking.
10. Design a System to Handle Millions of Requests per Second (Amazon) Problem: Scalable system design. Solution: Use load balancers, caching (Redis), sharding databases, microservices. Discuss trade-offs like consistency vs. availability (CAP theorem). Why asked: High-level design.
11. Explain How You Would Optimize a Slow-Running SQL Query (Microsoft) Problem: Query optimization. Solution: Analyze EXPLAIN, add indexes, avoid SELECT *, join efficiently, limit rows. Use profiling tools. Why asked: Database knowledge.
12. Design a Distributed Caching System (Google) Problem: Cache design. Solution: LRU eviction, consistent hashing for distribution, replication for fault tolerance. Handle cache misses with DB fallback. Why asked: Scalability.
13. Tell Me About a Time You Had to Make a Decision with Incomplete Information (Amazon) Problem: Behavioral. Solution: Use STAR: Situation (project deadline), Task (choose tech), Action (research pros/cons, consult team), Result (successful launch). Why asked: Leadership.
14. What is the Difference Between a Mutex and a Semaphore? (Microsoft) Problem: Concurrency. Solution: Mutex for mutual exclusion (ownership), semaphore for signaling (count-based). Mutex binary semaphore variant. Why asked: OS concepts.
15. Describe a Challenging Project You Worked On and How You Overcame Challenges (Google) Problem: Behavioral. Solution: STAR: Scaling app, bottlenecks in DB, optimized queries/sharded, reduced latency 50%. Why asked: Experience reflection.

These questions are drawn from real reports—e.g., Glassdoor users mention similar ones in 2025 interviews.

Preparation Tips for Each SDE Level

Success demands targeted practice. Here’s actionable advice:

• For SDE-1: Grind 75 LeetCode problems. Focus on basics via our DSA courses. Mock interviews on Pramp.
• For SDE-2: Master OOP and low-level design. Read “System Design Interview” by Alex Xu. Enroll in master DSA, web dev, and system design for comprehensive prep.
• For SDE-3: Practice high-level designs. Use Grokking the System Design Interview. Explore data science courses for advanced analytics.

General tips: Use STAR for behavioral, include metrics. Practice 4-5 hours daily. For quick boosts, try our crash course.

Expert quote: “The chief difference is the time you have to solve the problem. No real-world problem has to be solved in 20 minutes,” notes a Quora contributor on interview vs. real work.

Common Mistakes to Avoid in SDE Interviews

• Jumping into code without clarifying requirements (common in SDE-2).
• Ignoring edge cases in coding.
• Weak behavioral stories—always tie to impact.
• Overlooking soft skills for SDE-3.

Avoid these by practicing mocks and reviewing failures.

Final Thoughts and Next Steps

Mastering SDE levels means aligning prep with expectations—fundamentals for SDE-1, ownership for SDE-2, leadership for SDE-3. With dedication, you can crack these interviews. Ready to accelerate? Explore our courses and start today.

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