Detect permutation in matrix
Last updated: January 19, 2026
Quick Overview
Given a 2D matrix of characters and a string, determine if any of the rows or columns in the matrix contain a permutation of the given string. The function should return true if at least one permutation is found, and false otherwise. The input will consist of a matrix represented as a list of lists and a target string, with the output being a boolean value.
Stripe
January 19, 20261
10
803 solved
Given a 2D matrix of characters and a string, determine if any of the rows or columns in the matrix contain a permutation of the given string. The function should return true if at least one permutation is found, and false otherwise. The input will consist of a matrix represented as a list of lists and a target string, with the output being a boolean value.
Stripe uses this problem in the Phone 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 solve this iteratively instead of recursively (or vice versa)?
- How would you parallelize this solution?
- What is the worst-case input for your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To detect if any row or column in a 2D matrix contains a permutation of a given string, we can leverage the concept of frequency counting using hash maps. This problem can be viewed as a variation of ...
Approach
- Frequency Count of Target String: Create a frequency dictionary for the characters in the target string. For example, for the string 'abc', the frequency dictionary will be `{'a': 1, 'b': 1, 'c...
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