Transform linked list to adjacency list
Last updated: January 31, 2026
Quick Overview
Given a singly linked list where each node contains a value and a reference to a list of its neighbors, transform this linked list into an adjacency list representation. The output should be a dictionary where each key is a node's value and the corresponding value is a list of its neighbors' values. Ensure that the adjacency list accurately reflects the connections represented in the linked list.
Instacart
January 31, 202617
9
1,321 solved
Given a singly linked list where each node contains a value and a reference to a list of its neighbors, transform this linked list into an adjacency list representation. The output should be a dictionary where each key is a node's value and the corresponding value is a list of its neighbors' values. Ensure that the adjacency list accurately reflects the connections represented in the linked list.
This coding problem is frequently asked during Onsite at Instacart. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Instacart 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 in a single pass?
- What is the worst-case input for your solution?
- How would you parallelize this solution?
- Can you optimize the space complexity of your solution?
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Problem Analysis
To transform a singly linked list into an adjacency list representation, we will utilize the properties of linked lists and dictionaries in Python. Each node in the linked list contains a value and a ...
Approach
- Initialize an empty dictionary to hold the adjacency list.
- Start at the head of the linked list and iterate through each node.
- For each node, retrieve its value and its neighbors.
- For e...
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