Detect subsequence in matrix
Last updated: January 25, 2026
Quick Overview
Given a 2D matrix of characters and a string, determine if the string can be found as a subsequence in any of the rows or columns of the matrix. The function should return true if the subsequence exists and false otherwise. A subsequence is defined as a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements.
HashiCorp
January 25, 202641
8
1,715 solved
Given a 2D matrix of characters and a string, determine if the string can be found as a subsequence in any of the rows or columns of the matrix. The function should return true if the subsequence exists and false otherwise. A subsequence is defined as a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements.
This coding problem is frequently asked during Take-home Project at HashiCorp. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. HashiCorp 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
- What happens if the input contains duplicates?
- Can you optimize the space complexity of your solution?
- How would your solution change if the input was sorted?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to determine if a given string can be found as a subsequence in any row or column of a 2D matrix. The key to solving this problem is recognizing that we can utilize a two-point...
Approach
- Iterate through each row of the matrix: For each row, initialize two pointers: one for the row (
i) and one for the target string (j). - Check for subsequence: While iterating through ...
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