Optimize traversal for O(1) space
Last updated: May 2, 2026
Quick Overview
Given a binary tree, implement a traversal method that visits all nodes in the tree while using O(1) space. Your solution should not utilize any additional data structures, and you should return the values of the nodes in the order they are visited.
Booking.com
May 2, 202623
15
3,430 solved
Given a binary tree, implement a traversal method that visits all nodes in the tree while using O(1) space. Your solution should not utilize any additional data structures, and you should return the values of the nodes in the order they are visited.
Booking.com uses this problem in the Technical 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
- How would you parallelize this solution?
- How would you modify your solution to handle streaming input?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to traverse a binary tree in an O(1) space complexity manner. This suggests that we cannot use any additional data structures like stacks or queues, which are commonly used in ...
Approach
- Initialize Current Node: Start with the root node of the binary tree.
- Iterate through the Tree: While the current node is not null:
- If the current node has a left child:
- Find...
- If the current node has a left child:
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