Optimize traversal for O(n) time
Last updated: August 6, 2025
Quick Overview
Given a binary tree, implement a traversal algorithm that visits each node in O(n) time while optimizing for space usage. Your solution should return the values of the nodes in an array in the order they are visited. Ensure that your approach does not use additional data structures that exceed O(1) space complexity.
Vercel
August 6, 2025583
13
2,748 solved
Given a binary tree, implement a traversal algorithm that visits each node in O(n) time while optimizing for space usage. Your solution should return the values of the nodes in an array in the order they are visited. Ensure that your approach does not use additional data structures that exceed O(1) space complexity.
Vercel 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
- 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?
- What is the worst-case input for your solution?
- Can you optimize the space complexity of your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we need to traverse a binary tree and return the values in the order they are visited while ensuring the time complexity is O(n) and space complexity is O(1) (not counting the space u...
Approach
To implement Morris Traversal, we will follow these steps:
- Start at the root node of the tree.
- While the current node is not null, check if it has a left child.
- If it does, find the rightmo...
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