Transform linked list to hash map
Last updated: February 20, 2026
Quick Overview
Given a linked list, transform it into a hash map where each key is the value of a node in the linked list and the corresponding value is the number of times that node's value appears in the list. The function should take the head of the linked list as input and return the resulting hash map. Ensure that the solution efficiently handles large linked lists.
Vercel
February 20, 2026137
9
3,960 solved
Given a linked list, transform it into a hash map where each key is the value of a node in the linked list and the corresponding value is the number of times that node's value appears in the list. The function should take the head of the linked list as input and return the resulting hash map. Ensure that the solution efficiently handles large linked lists.
This coding problem is frequently asked during Onsite at Vercel. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Vercel 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
- What is the worst-case input for your solution?
- What if the input doesn't fit in memory?
- How would you modify your solution to handle streaming input?
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Problem Analysis
The problem requires us to traverse a linked list and create a hash map (dictionary in Python) where each key is a node's value and each value is the count of how many times that value appears in the ...
Approach
- Initialize an empty hash map (dictionary) to store the counts.
- Start traversing the linked list from the head node.
- For each node, check if its value is already a key in the hash map:
- If...
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