Transform linked list to hash map
Last updated: November 17, 2025
Quick Overview
Given a linked list, transform it into a hash map where each key is the value of a node and the corresponding value is the number of times that value appears in the linked list. Your function should take the head of the linked list as input and return the resulting hash map.
Dropbox
November 17, 2025110
10
3,112 solved
Given a linked list, transform it into a hash map where each key is the value of a node and the corresponding value is the number of times that value appears in the linked list. Your function should take the head of the linked list as input and return the resulting hash map.
Dropbox uses this problem in the Technical 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
- 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
- How would your solution change if the input was sorted?
- What happens if the input contains duplicates?
- Can you solve this iteratively instead of recursively (or vice versa)?
- How would you test this solution thoroughly?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of transforming a linked list into a hash map, we need to recognize that the task involves counting occurrences of each unique value in the linked list. This scenario is best appr...
Approach
- Initialize a Hash Map: Create an empty dictionary to hold the counts of each value.
- Traverse the Linked List: Start from the head of the linked list and iterate through each node.
- F...
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