Optimize traversal for in-place
Last updated: August 24, 2025
Quick Overview
Given a binary tree, implement an in-place traversal algorithm that optimizes the order of node visits without using additional data structures. Your solution should modify the tree structure to achieve the desired traversal order and return the root of the modified tree. The expected output is the root node after the traversal has been completed.
Shopify
August 24, 2025224
10
1,473 solved
Given a binary tree, implement an in-place traversal algorithm that optimizes the order of node visits without using additional data structures. Your solution should modify the tree structure to achieve the desired traversal order and return the root of the modified tree. The expected output is the root node after the traversal has been completed.
Shopify 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
- How would you test this solution thoroughly?
- What happens if the input contains duplicates?
- How would you modify your solution to handle streaming input?
- How would your solution change if the input was sorted?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to perform an in-place traversal of a binary tree and optimize the order of node visits without utilizing additional data structures. This suggests we need to manipulate the tr...
Approach
- Choose a Traversal Method: We will use the Morris Traversal technique, which allows us to traverse the tree in-order without using additional space. This method temporarily modifies the tree st...
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