Transform matrix to adjacency list
Last updated: September 28, 2025
Quick Overview
Given a matrix representing a graph where each element indicates the presence of an edge between nodes, transform this matrix into an adjacency list. The input will be a 2D array of integers, and the output should be a list of lists where each inner list contains the neighbors of the corresponding node. Ensure that the adjacency list accurately reflects the connections represented in the matrix.
568
4
622 solved
Given a matrix representing a graph where each element indicates the presence of an edge between nodes, transform this matrix into an adjacency list. The input will be a 2D array of integers, and the output should be a list of lists where each inner list contains the neighbors of the corresponding node. Ensure that the adjacency list accurately reflects the connections represented in the matrix.
Reddit uses this problem in the Phone Screen 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
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
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
- Can you solve this iteratively instead of recursively (or vice versa)?
- What is the worst-case input for your solution?
- How would you modify your solution to handle streaming input?
- How would you parallelize this solution?
Sharpen Your Skills on Codemia
Practice similar problems with our interactive workspace, get AI feedback, and track your progress.
Practice DSA ProblemsSample Answer
Problem Analysis
The problem involves transforming a matrix representation of a graph into an adjacency list. Each element in the matrix indicates whether there is an edge between nodes, where a value of 1 signifies a...
Approach
- Initialize an empty list of lists for the adjacency list, where the outer list corresponds to each node in the graph.
- Iterate through the rows of the matrix. For each row (representing a node),...
Submit Your Answer
