Optimize traversal for without recursion
Last updated: January 31, 2026
Quick Overview
Given a binary tree, implement a function to traverse the tree in pre-order without using recursion or a stack. Your solution should return the values of the nodes in a list, maintaining the order of traversal. Ensure that your implementation operates within O(n) time complexity, where n is the number of nodes in the tree.
Rippling
January 31, 2026252
8
2,616 solved
Given a binary tree, implement a function to traverse the tree in pre-order without using recursion or a stack. Your solution should return the values of the nodes in a list, maintaining the order of traversal. Ensure that your implementation operates within O(n) time complexity, where n is the number of nodes in the tree.
Rippling 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
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
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 in a single pass?
- How would you modify your solution to handle streaming input?
- How would your solution change if the input was sorted?
- Can you optimize the space complexity of your solution?
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Problem Analysis
This problem requires us to perform a pre-order traversal of a binary tree without using recursion or a stack. The pre-order traversal visits nodes in the order: root, left, right. Since we cannot use...
Approach
- Start at the root of the tree.
- While the current node is not null:
- If the current node has no left child, visit the node (add its value to the result list) and move to the right child. ...
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