Optimize traversal for in-place
Last updated: January 3, 2026
Quick Overview
Given a binary tree, write a function to optimize the in-place traversal of the tree using O(1) space. The function should visit each node in the tree and print its value in pre-order (root, left, right) without using any additional data structures for storing nodes.
Capital One
January 3, 202639
10
3,863 solved
Given a binary tree, write a function to optimize the in-place traversal of the tree using O(1) space. The function should visit each node in the tree and print its value in pre-order (root, left, right) without using any additional data structures for storing nodes.
Capital One 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
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
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?
- Can you solve this in a single pass?
- What happens if the input contains duplicates?
- How would you modify your solution to handle streaming input?
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Problem Analysis
To solve the problem of in-place traversal of a binary tree using O(1) space, we can utilize the Morris Traversal technique. This method allows us to traverse the tree without using a stack or rec...
Approach
- Start at the root of the tree.
- While the current node is not null:
- If the current node has no left child, print its value and move to the right child.
- If the current node has a left ch...
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