Find longest subsequence in linked list
Last updated: July 8, 2025
Quick Overview
Given a linked list, write a function to find the longest subsequence of elements that are in increasing order. The function should return the length of this longest increasing subsequence. The input will be the head of the linked list, and the output should be an integer representing the length of the subsequence.
Grubhub
July 8, 202530
8
306 solved
Given a linked list, write a function to find the longest subsequence of elements that are in increasing order. The function should return the length of this longest increasing subsequence. The input will be the head of the linked list, and the output should be an integer representing the length of the subsequence.
Coding interviews at Grubhub 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
- What happens if the input contains duplicates?
- How would you modify your solution to handle streaming input?
- What is the worst-case input for your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To find the longest increasing subsequence (LIS) in a linked list, we need to recognize the problem as a dynamic programming challenge rather than a simple traversal or searching problem. The LIS is n...
Approach
- Convert the Linked List to an Array: First, traverse the linked list and store its elements in an array. This allows us to easily access elements by index, which is crucial for implementing the...
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