Find cycle in matrix
Last updated: January 10, 2026
Quick Overview
Given a 2D matrix filled with characters, write a function to determine if there exists a cycle in the matrix, where a cycle is defined as a path that starts and ends at the same cell, moving only through adjacent cells (up, down, left, right) with the same character. The function should return true if a cycle is found and false otherwise.
Dropbox
January 10, 202660
4
1,207 solved
Given a 2D matrix filled with characters, write a function to determine if there exists a cycle in the matrix, where a cycle is defined as a path that starts and ends at the same cell, moving only through adjacent cells (up, down, left, right) with the same character. The function should return true if a cycle is found and false otherwise.
Coding interviews at Dropbox 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
- What if the input doesn't fit in memory?
- Can you solve this in a single pass?
- Can you optimize the space complexity of your solution?
- How would you modify your solution to handle streaming input?
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Problem Analysis
The problem requires us to determine if there exists a cycle in a 2D matrix of characters. A cycle is defined as a path that starts and ends at the same cell, using adjacent cells with the same charac...
Approach
- Initialize a Visited Matrix: Create a 2D list to track visited cells.
- Iterate Over Each Cell: For each cell in the matrix, if it hasn't been visited, initiate a DFS from that cell.
- ...
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