Transform linked list to adjacency list
Last updated: January 21, 2026
Quick Overview
Given a singly linked list where each node contains a value and a reference to the next node, transform this linked list into an adjacency list representation of a graph. Each node's value should be used as a key in the adjacency list, with its corresponding value being a list of all the nodes it is directly connected to. The output should be a dictionary where each key is a node's value and the value is a list of connected nodes' values.
Notion
January 21, 202610
3
4,958 solved
Given a singly linked list where each node contains a value and a reference to the next node, transform this linked list into an adjacency list representation of a graph. Each node's value should be used as a key in the adjacency list, with its corresponding value being a list of all the nodes it is directly connected to. The output should be a dictionary where each key is a node's value and the value is a list of connected nodes' values.
This coding problem is frequently asked during Phone Screen at Notion. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Notion expects candidates to write production-quality code, not just solve the puzzle.
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
- Can you solve this iteratively instead of recursively (or vice versa)?
- What is the worst-case input for your solution?
- What happens if the input contains duplicates?
- What if the input doesn't fit in memory?
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Problem Analysis
The problem requires transforming a singly linked list into an adjacency list representation of a graph. Each node in the linked list has a value and a reference to the next node. Thus, the adjacency ...
Approach
- Initialize an empty dictionary to store the adjacency list.
- Traverse the linked list starting from the head node.
- For each node, check if it has a next node:
- If it does, ad...
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