Detect subsequence in matrix
Last updated: May 18, 2026
Quick Overview
Given a 2D matrix of characters and a target string, determine if the target string can be formed as a subsequence by traversing the matrix in a continuous path (up, down, left, right). The function should return true if the subsequence exists and false otherwise. The input will consist of the matrix dimensions and the target string, and the output will be a boolean value.
Coinbase
May 18, 20262
6
4,084 solved
Given a 2D matrix of characters and a target string, determine if the target string can be formed as a subsequence by traversing the matrix in a continuous path (up, down, left, right). The function should return true if the subsequence exists and false otherwise. The input will consist of the matrix dimensions and the target string, and the output will be a boolean value.
Coding interviews at Coinbase 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
- 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 parallelize this solution?
- How would you modify your solution to handle streaming input?
- What is the worst-case input for your solution?
- What happens if the input contains duplicates?
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Problem Analysis
To determine if a target string can be formed as a subsequence by traversing a 2D matrix of characters, we can utilize Depth-First Search (DFS). This approach is suitable because we need to explore al...
Approach
- Start by iterating through each cell in the matrix. For each cell, check if it matches the first character of the target string.
- If it matches, initiate a DFS from that cell, passing the current...
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