Transform array to adjacency list
Last updated: August 21, 2025
Quick Overview
Given an array of edges representing a graph, transform it into an adjacency list representation. Each edge is defined by a pair of vertices, and the output should be a list where each index corresponds to a vertex and contains a list of its adjacent vertices. Ensure that the adjacency list is constructed efficiently and handles cases with multiple edges and disconnected components.
TikTok
August 21, 20251
3
3,052 solved
Given an array of edges representing a graph, transform it into an adjacency list representation. Each edge is defined by a pair of vertices, and the output should be a list where each index corresponds to a vertex and contains a list of its adjacent vertices. Ensure that the adjacency list is constructed efficiently and handles cases with multiple edges and disconnected components.
TikTok 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
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
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 your solution change if the input was sorted?
- What is the worst-case input for your solution?
- Can you solve this in a single pass?
- Can you optimize the space complexity of your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To transform the given array of edges into an adjacency list, we can identify that this problem requires a mapping of vertices to their respective adjacent vertices. The suitable algorithmic pattern h...
Approach
- Initialize an empty dictionary
adjacency_listto store the adjacency list. - Iterate over each edge in the input array. For each edge
(u, v), do the following:- If
uis not in `adjacency...
- If
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