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This is a medium difficulty Coding & Algorithms question, commonly asked during Onsite rounds at Google.

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This question is commonly asked for Software Engineer candidates at Google during technical interviews.

Group movies via graph traversal

Last updated: Mar 29, 2026

Quick Overview

This question evaluates graph traversal and connectivity skills, specifically competence with BFS, DFS (iterative and recursive), complexity analysis, and Union-Find for identifying connected components in an undirected graph.

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Group movies via graph traversal

Google

Sep 6, 2025, 12:00 AM

mediumSoftware EngineerOnsiteCoding & Algorithms

You are given n movies labeled 0..n-1 and a list of undirected pairs (a, b) meaning movies a and b are similar. Group all movies into categories where each category is a maximal set of movies connected via similarity links (i.e., connected components). Return the categories as lists of movie IDs, each list sorted, and the collection sorted by the smallest ID in each category. Implement solutions using both BFS and DFS, explain their time/space complexity, and compare iterative vs. recursive DFS. Then discuss an alternative Union-Find approach and when it would be preferable. Dry-run on n=8 with pairs: (0, 1),(1, 2),(3, 4),(5, 6),(6, 7).