Find connected components in graph
Last updated: December 13, 2025
Quick Overview
Given an undirected graph represented as an adjacency list, write a function to find all connected components in the graph. The function should return a list of lists, where each inner list contains the nodes of a connected component. The input will be a dictionary where keys are node identifiers and values are lists of adjacent nodes.
Square/Block
December 13, 20252
3
3,504 solved
Given an undirected graph represented as an adjacency list, write a function to find all connected components in the graph. The function should return a list of lists, where each inner list contains the nodes of a connected component. The input will be a dictionary where keys are node identifiers and values are lists of adjacent nodes.
Square/Block uses this problem in the Onsite to evaluate your algorithmic thinking. They expect you to discuss multiple approaches, analyze trade-offs between them, and implement the optimal solution with clean, readable code.
What the Interviewer Expects
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would you parallelize this solution?
- How would you test this solution thoroughly?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to find all connected components in an undirected graph represented as an adjacency list. A connected component is a subset of the graph where there exists a path between any t...
Approach
- Initialize a visited set to keep track of all the nodes we've explored.
- Iterate through each node in the adjacency list. If the node has not been visited, initiate a new DFS/BFS to exp...
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