Detect palindrome in matrix
Last updated: January 1, 2026
Quick Overview
Given a 2D matrix of characters, write a function to detect all palindromic sequences of a specified length within the matrix. The function should return a list of the starting coordinates (row, column) of each palindromic sequence found, considering horizontal, vertical, and diagonal directions. The input will include the matrix and the length of the palindrome to search for, while the output will be a list of tuples representing the coordinates.
Robinhood
January 1, 202646
4
2,973 solved
Given a 2D matrix of characters, write a function to detect all palindromic sequences of a specified length within the matrix. The function should return a list of the starting coordinates (row, column) of each palindromic sequence found, considering horizontal, vertical, and diagonal directions. The input will include the matrix and the length of the palindrome to search for, while the output will be a list of tuples representing the coordinates.
Coding interviews at Robinhood 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
- Can you solve this iteratively instead of recursively (or vice versa)?
- How would your solution change if the input was sorted?
- Can you optimize the space complexity of your solution?
- What if the input doesn't fit in memory?
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Problem Analysis
To detect palindromic sequences in a 2D matrix, we can leverage a traversal method that explores all possible directions (horizontal, vertical, and diagonal). The challenge is to efficiently check for...
Approach
- Input Validation: Ensure the matrix is not empty and the specified palindrome length is valid (greater than 1 and less than or equal to the maximum dimension of the matrix).
- **Initialize Res...
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