Detect subsequence in linked list
Last updated: December 9, 2025
Quick Overview
Given a linked list and a sequence of values, determine if the sequence exists as a subsequence within the linked list. The function should return true if the subsequence is found and false otherwise. The input will be a linked list head and an array of values representing the subsequence to detect.
ServiceNow
December 9, 202514
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3,535 solved
Given a linked list and a sequence of values, determine if the sequence exists as a subsequence within the linked list. The function should return true if the subsequence is found and false otherwise. The input will be a linked list head and an array of values representing the subsequence to detect.
Coding interviews at ServiceNow focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
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 you parallelize this solution?
- Can you optimize the space complexity of your solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to check if a given sequence of values exists as a subsequence in a linked list. The key aspect here is understanding what constitutes a subsequence: it means that the elements...
Approach
- Initialize two pointers: one for the linked list (
current_node) starting at the head, and another for the sequence (seq_index) starting at the beginning of the sequence array. - Traverse thr...
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