Find cycle in matrix
Last updated: July 27, 2025
Quick Overview
Given a matrix of integers, 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 in four possible directions (up, down, left, right) and visiting adjacent cells with the same value. The function should return true if such a cycle exists, and false otherwise.
Waymo
July 27, 202516
15
4,449 solved
Given a matrix of integers, 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 in four possible directions (up, down, left, right) and visiting adjacent cells with the same value. The function should return true if such a cycle exists, and false otherwise.
Coding interviews at Waymo 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
- Can you optimize the space complexity of your solution?
- How would you test this solution thoroughly?
- How would your solution change if the input was sorted?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we need to detect if there exists a cycle in a matrix where the cycle consists of adjacent cells with the same value. The best approach for this problem is Depth-First Search (DFS) si...
Approach
- Initialization: Start by creating a visited matrix of the same dimensions as the input matrix to keep track of cells that have been explored. 2. DFS Function: Define a recursive DFS functio...
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