Optimize traversal for O(1) space
Last updated: August 15, 2025
Quick Overview
Given a binary tree, implement an algorithm to traverse the tree in-order while using O(1) space. You should not use any additional data structures for storing nodes, and your solution should modify the tree structure temporarily if necessary. The output should be the values of the nodes in the order they are visited.
SpaceX
August 15, 2025226
9
419 solved
Given a binary tree, implement an algorithm to traverse the tree in-order while using O(1) space. You should not use any additional data structures for storing nodes, and your solution should modify the tree structure temporarily if necessary. The output should be the values of the nodes in the order they are visited.
Coding interviews at SpaceX 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 iteratively instead of recursively (or vice versa)?
- Can you solve this in a single pass?
- What if the input doesn't fit in memory?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we need to perform an in-order traversal of a binary tree using O(1) space. The key here is to recognize that we cannot use any additional data structures, such as stacks or lists, to...
Approach
The Morris Traversal algorithm for in-order traversal can be broken down into the following steps:
- Start at the root of the tree.
- While the current node is not null:
- If the current node has...
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