Detect subsequence in linked list
Last updated: November 19, 2025
Quick Overview
Given a linked list and a sequence of integers, determine if the sequence appears as a subsequence within the linked list. A subsequence is defined as a sequence that can be derived from the linked list by deleting some elements without changing the order of the remaining elements. Return true if the subsequence exists, and false otherwise.
Redfin
November 19, 20257
5
1,791 solved
Given a linked list and a sequence of integers, determine if the sequence appears as a subsequence within the linked list. A subsequence is defined as a sequence that can be derived from the linked list by deleting some elements without changing the order of the remaining elements. Return true if the subsequence exists, and false otherwise.
This coding problem is frequently asked during Phone Screen at Redfin. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Redfin 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
- How would you modify your solution to handle streaming input?
- Can you optimize the space complexity of your solution?
- How would your solution change if the input was sorted?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if a given sequence of integers appears as a subsequence within a linked list, we can utilize the two-pointer technique. This approach is applicable here because we can traverse the linke...
Approach
- Initialize two pointers: one for the linked list (
current) and one for the sequence (seq_index). - Iterate through the linked list using the
currentpointer. - For each node in the linked l...
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