Google Software Engineer L3 Interview Questions (2025)

What Is Google L3?

The L3 Interview Loop

RoundFormatDuration Coding Round 1Algorithm & data structures45 min Coding Round 2Algorithm & data structures45 min GoogleynessBehavioural & culture fit45 min System DesignUsually light for L345 min (optional)

Note: Some L3 loops skip system design entirely. Whether it's included depends on the team and your experience level.

Real Google L3 Coding Questions (Reported 2023–2025)

Arrays & Hashing

1. Two Sum (and its variants)

2. Group Anagrams

Follow-up: optimise from O(n·k log k) to O(n·k) using character frequency as the key.

3. Longest Consecutive Sequence

4. Product of Array Except Self

Strings & Sliding Window

5. Minimum Window Substring

This is a Google favourite. Master the two-pointer + frequency map pattern.

6. Longest Substring Without Repeating Characters

7. Valid Parentheses / Generate Parentheses

Trees & Graphs

8. Binary Tree Level Order Traversal

9. Lowest Common Ancestor of a BST / Binary Tree

10. Word Ladder

11. Number of Islands / Connected Components

12. Course Schedule (Topological Sort)

Dynamic Programming

13. Coin Change

14. Longest Common Subsequence

15. Jump Game I & II

16. Decode Ways

Heaps & Priority Queues

17. Merge K Sorted Lists

18. Top K Frequent Elements

19. Find Median from Data Stream

Design & OOP (Less Common at L3)

20. Design a LRU Cache

21. Design a Parking Lot

Google L3 Behavioural Questions

*"Tell me about a time you had a disagreement with a team member. How did you resolve it?"*
*"Describe a project you're most proud of. What was your specific contribution?"*
*"Give me an example of when you had to learn something new quickly."*
*"Tell me about a time you made a mistake. What did you do?"*
*"Describe a situation where you had to work with ambiguous requirements."*

STAR Format:

Situation — set the scene

Task — what you were responsible for

Action — exactly what *you* did (not "we")

Result — measurable impact

Google Differentiator: Google specifically values intellectual humility. Answers that show you learned from failure score higher than heroic "I saved the day" stories.

L3 System Design (If It Comes Up)

Clarify requirements and define scale (users/QPS/storage)
Sketch a simple high-level architecture (client, API server, database)
Explain basic caching and when you'd use it
Discuss database choice (SQL vs NoSQL) with rationale
Identify one or two bottlenecks and how to address them

Common L3 System Design Topics:

Design a URL shortener
Design a key-value store
Design a notification service
Design a rate limiter

Google L3 Preparation Timeline

WeekFocus 1–2Arrays, strings, sliding window 3–4Trees, graphs, BFS/DFS 5–6DP, heaps, tries 7Mock interviews, timed practice 8Behavioural stories, system design basics

Interview-Day Execution Framework

Listen fully before repeating the problem in your own words
Ask 2–3 clarifying questions (input constraints, edge cases, return type)
State your approach and complexity before typing a single line
Code with narration — explain what each section does
Test your code with the given example, then an edge case (empty input, single element)
Optimise only if asked — a clean correct solution beats a clever broken one

How Topalupu Helps You Crack L3

Problems matched to the exact L3 question bank above
AI mock coding interviews with a Google engineer persona and real-time feedback
Behavioural sessions scored using the STAR framework
System design walkthroughs targeted at L3 expectations