Detect subsequence in matrix
Last updated: August 7, 2025
Quick Overview
Given a 2D matrix of characters and a string, determine if the string can be formed as a subsequence by traversing the matrix in a left-to-right and top-to-bottom manner. The function should return true if the subsequence exists, and false otherwise. The input consists of the matrix dimensions and the string, while the output is a boolean value indicating the presence of the subsequence.
Square/Block
August 7, 202596
10
666 solved
Given a 2D matrix of characters and a string, determine if the string can be formed as a subsequence by traversing the matrix in a left-to-right and top-to-bottom manner. The function should return true if the subsequence exists, and false otherwise. The input consists of the matrix dimensions and the string, while the output is a boolean value indicating the presence of the subsequence.
Square/Block uses this problem in the Technical Screen to evaluate your algorithmic thinking. They expect you to discuss multiple approaches, analyze trade-offs between them, and implement the optimal solution with clean, readable code.
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
- Can you optimize the space complexity of your solution?
- How would you test this solution thoroughly?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we need to determine if a given string can be formed as a subsequence by navigating through a 2D matrix of characters. The key constraint is that we can only traverse the matrix in a ...
Approach
- Initialization: Start by checking if the string is empty. If it is, return true since an empty string is trivially a subsequence. If the matrix is empty or the string is longer than the total n...
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