Google Interview Questions 2026

Given a binary tree, return the boundary of the tree in anti-clockwise direction starting from the root. The boundary consists of the left boundary, leaves, and the right boundary in reverse.

Implement Dijkstra's algorithm using a Fibonacci heap. Compare amortized complexity with a binary heap and explain when the Fibonacci heap is actually slower in practice despite the better theoretical bound.

Implement a topological sort for a directed acyclic graph. Then extend it to detect cycles and explain how this maps to dependency resolution in build systems like Bazel.

Given a large dependency graph of build targets, design an algorithm to compute the minimal set of targets that need to be rebuilt after a file changes, and explain how you would parallelize the rebuild across workers respecting dependency order.

Tell me about a time you had a strong technical disagreement with a senior engineer. How did you handle it, and what was the outcome? Be specific about the technical context and your reasoning.

Google values "Googleyness". Describe a situation where you went significantly beyond your role to help a colleague or improve something that was not your responsibility.

Tell me about a time your code caused a production incident. What was your immediate response, and what did you change afterward so it wouldn't happen again?

Design Google Search autocomplete. As a user types "wea", suggest "weather", "weather today", "weather London". Cover: trie vs inverted index, personalisation, freshness, latency budget (<100ms), and how you handle offensive query suggestions.

Design Google Maps ETA calculation. How do you compute the fastest route for 1B+ users in real time? Cover: graph representation of road network, Dijkstra vs A* vs Contraction Hierarchies, live traffic data ingestion, and how you handle road closures.

Design Bigtable or a wide-column store from scratch. Explain SSTable, memtable, compaction strategies (size-tiered vs levelled), bloom filters for read optimisation, and how you handle tombstones for deletes.

Design a URL shortening service (like bit.ly) that handles 1 billion shortened URLs and 100K redirects per second.

Given a list of intervals, merge all overlapping intervals and return the result. Explain the sort-then-scan approach and the edge cases (touching intervals, single interval, all disjoint).

Explain how a browser renders a web page from the moment the user presses Enter. Cover: DNS resolution, TCP handshake, HTTP request, HTML parsing, CSSOM, render tree, layout, paint, and compositing. Where would you optimise for Core Web Vitals?

Our RAG pipeline responses are accurate in staging but hallucinate in production on long user queries. Walk me through how you debug and fix this.

A list of 50,000 items renders in a React component. Users scroll and experience jank. How do you fix it without pagination?

You're building a real-time collaborative document editor (like Google Docs) in React. Multiple users edit simultaneously. How do you handle state synchronization without the UI flickering or losing cursor position?

Explain how React's reconciliation algorithm decides what to re-render. A senior dev claims 'adding a key prop always makes things faster.' Is he right?

Design Google Drive's file sync system. A file changed on desktop must appear on mobile within 5 seconds. Files can be up to 10GB. Handle 100 million users.

Design a search autocomplete system (like Google's search bar). It must return results in under 50ms, handle 100,000 queries per second, and personalize results based on user history.

Design an autocomplete/typeahead system for a search engine handling 100K queries per second. Discuss the trie-based approach, how you would rank suggestions, and how you would keep the trie updated with trending queries without hurting read latency.

Design YouTube's video upload and processing pipeline. A user uploads a 4K video of 10GB. How does it become available in 360p, 720p, and 4K for streaming?

Implement a trie data structure. Your implementation must support: insert, search, and startsWith. Then optimize space for a dictionary with 1 million words.

How would you design and implement an autocomplete system? Focus on the data structure and ranking.

Your gRPC service has p99 latency of 1 second. Adding a timeout of 500ms seems to help p99 but now 1% of requests fail with DeadlineExceeded. What's the correct approach?

Design the backend for a Google Maps-like routing service with real-time traffic.

Design a real-time collaborative whiteboard like Miro where multiple users draw simultaneously.

Explain gRPC vs REST API. When would you choose gRPC?

Explain the difference between reconciliation and the commit phase in React. Why can render be interrupted in Concurrent Mode but commit cannot?

You have a 50GB CSV file and only 8GB of RAM. Walk through how you would compute the average of one column using pandas without crashing the process.

Design a URL shortener that must handle 100M new URLs per day and 10x that in reads. Walk through your ID generation strategy and why a simple auto-increment counter breaks at this scale.