Optimize traversal for without recursion
Last updated: May 17, 2026
Quick Overview
Given a binary tree, implement a function to traverse the tree in-order without using recursion or a stack. Your solution should modify the tree structure minimally and return the values in an array in the order they were visited. The function should handle edge cases, including empty trees and trees with only one node.
Palantir
May 17, 2026143
13
2,038 solved
Given a binary tree, implement a function to traverse the tree in-order without using recursion or a stack. Your solution should modify the tree structure minimally and return the values in an array in the order they were visited. The function should handle edge cases, including empty trees and trees with only one node.
Coding interviews at Palantir 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
- 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
- What is the worst-case input for your solution?
- Can you solve this in a single pass?
- Can you optimize the space complexity of your solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Problem Analysis
To traverse a binary tree in-order (left, root, right) without using recursion or a stack, we can utilize the concept of Morris Traversal. This approach modifies the tree structure minimally by creati...
Approach
- Start at the root of the binary tree.
- While the current node is not null:
- If the current node has no left child, add its value to the result and move to the right child.
- If the current...
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