Detect permutation in linked list
Last updated: December 19, 2025
Quick Overview
Given two linked lists, determine if one linked list is a permutation of the other. You should implement a function that takes the heads of both linked lists as input and returns a boolean indicating whether the second linked list is a permutation of the first. The solution should consider the order of elements and handle cases with varying lengths appropriately.
Waymo
December 19, 20252
4
1,969 solved
Given two linked lists, determine if one linked list is a permutation of the other. You should implement a function that takes the heads of both linked lists as input and returns a boolean indicating whether the second linked list is a permutation of the first. The solution should consider the order of elements and handle cases with varying lengths appropriately.
This coding problem is frequently asked during Onsite at Waymo. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Waymo expects candidates to write production-quality code, not just solve the puzzle.
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
- Can you solve this iteratively instead of recursively (or vice versa)?
- Can you optimize the space complexity of your solution?
- What is the worst-case input for your solution?
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Problem Analysis
To determine if one linked list is a permutation of another, we need to ensure both linked lists contain the same elements in the same frequency. A suitable pattern for this problem is the **hash tabl...
Approach
- Count Elements: First, traverse the first linked list and count the occurrences of each element using a hash table (or dictionary in Python).
Example: For linked list A: 1 -> 2 -> 2 -> 3, ...
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