Detect palindrome in matrix
Last updated: December 5, 2025
Quick Overview
Given a 2D matrix of characters, write a function to detect all occurrences of palindromic sequences in the matrix. A palindrome is a sequence that reads the same forwards and backwards, and you should consider horizontal, vertical, and diagonal sequences of at least three characters. The function should return a list of the starting coordinates of each detected palindrome along with the palindrome itself.
PlanetScale
December 5, 20257
12
223 solved
Given a 2D matrix of characters, write a function to detect all occurrences of palindromic sequences in the matrix. A palindrome is a sequence that reads the same forwards and backwards, and you should consider horizontal, vertical, and diagonal sequences of at least three characters. The function should return a list of the starting coordinates of each detected palindrome along with the palindrome itself.
This coding problem is frequently asked during Take-home Project at PlanetScale. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. PlanetScale 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
- Can you optimize the space complexity of your solution?
- How would you parallelize this solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to detect palindromic sequences in a 2D matrix. A palindrome reads the same forwards and backwards. Given that we need to consider horizontal, vertical, and diagonal sequences,...
Approach
We will implement the following steps to solve the problem:
- Iterate through each cell in the matrix. For each cell, we will check for palindromic sequences starting from that cell in four direc...
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