Transform matrix to adjacency list
Last updated: April 19, 2026
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 representation. The input will be a 2D array of integers, and the output should be a list of lists, where each sublist contains the neighbors of the corresponding node. Ensure the adjacency list accurately reflects the connections defined by the matrix.
Spotify
April 19, 2026263
10
197 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 representation. The input will be a 2D array of integers, and the output should be a list of lists, where each sublist contains the neighbors of the corresponding node. Ensure the adjacency list accurately reflects the connections defined by the matrix.
This coding problem is frequently asked during Phone Screen at Spotify. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Spotify expects candidates to write production-quality code, not just solve the puzzle.
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
- How would you modify your solution to handle streaming input?
- Can you solve this iteratively instead of recursively (or vice versa)?
- What if the input doesn't fit in memory?
- How would you test this solution thoroughly?
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Practice DSA ProblemsSample Answer
Problem Analysis
We are tasked with transforming a matrix representation of a graph into an adjacency list form. The matrix is a 2D array where matrix[i][j] indicates an edge from node i to node j. This problem ...
Approach
- Initialize an empty list
adjacency_listto store the neighbors for each node. - Loop through each row of the matrix using an index
i. For eachi, initialize an empty listneighbors. - L...
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