Transform array to adjacency list
Last updated: May 21, 2026
Quick Overview
Given an array of edges, where each edge is represented as a pair of vertices, transform this array into an adjacency list representation of a graph. The output should be a dictionary where each key is a vertex and the corresponding value is a list of adjacent vertices. Ensure that the adjacency list is constructed correctly, reflecting all connections from the input edges.
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May 21, 202678
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Given an array of edges, where each edge is represented as a pair of vertices, transform this array into an adjacency list representation of a graph. The output should be a dictionary where each key is a vertex and the corresponding value is a list of adjacent vertices. Ensure that the adjacency list is constructed correctly, reflecting all connections from the input edges.
Coding interviews at ServiceNow focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
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)?
- How would you parallelize this solution?
- What if the input doesn't fit in memory?
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Problem Analysis
The task is to convert an array of edges into an adjacency list representation of a graph. This problem is fundamentally about graph representation and we can use a dictionary to store each vertex as ...
Approach
- Initialize an empty dictionary called
adjacency_list. - Iterate through each edge in the input array. Each edge is a pair of vertices, say
(u, v). - For each vertex
u, check if it exist...
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