Optimize traversal for O(n) time
Last updated: March 20, 2026
Quick Overview
Given a binary tree, implement a traversal algorithm that visits each node in O(n) time complexity while ensuring that the space used is minimized. Your solution should return the values of the nodes in an array format as output.
Rippling
March 20, 202612
7
2,626 solved
Given a binary tree, implement a traversal algorithm that visits each node in O(n) time complexity while ensuring that the space used is minimized. Your solution should return the values of the nodes in an array format as output.
Coding interviews at Rippling 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
- Can you solve this in a single pass?
- How would you parallelize this solution?
- What is the worst-case input for your solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Problem Analysis
The problem requires us to traverse a binary tree in O(n) time while minimizing space complexity. A suitable pattern for this traversal is the Morris Traversal, which utilizes the concept of threa...
Approach
- Initialize a current pointer to the root of the tree.
- While the current pointer is not null, do the following:
- If the current node has no left child, visit the node (add its v...
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