Find cycle in binary tree
Last updated: December 28, 2025
Quick Overview
Given a binary tree, determine if it contains a cycle by checking for any nodes that are revisited during a traversal. Your function should return a boolean value: true if a cycle exists, and false otherwise. The solution should efficiently handle the traversal of the tree without using extra space for visited nodes.
Robinhood
December 28, 2025392
3
4,148 solved
Given a binary tree, determine if it contains a cycle by checking for any nodes that are revisited during a traversal. Your function should return a boolean value: true if a cycle exists, and false otherwise. The solution should efficiently handle the traversal of the tree without using extra space for visited nodes.
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
- How would you test this solution thoroughly?
- How would you modify your solution to handle streaming input?
- Can you optimize the space complexity of your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if a binary tree contains a cycle, we need to identify any nodes that are revisited during a traversal. In a typical binary tree, nodes are unique; however, if the tree structure allows f...
Approach
- DFS Traversal: We will perform a Depth-First Search on the binary tree. This involves recursively visiting each node and keeping track of the nodes that have been visited.
- **Parent Tracking...
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