Optimize traversal for without recursion
Last updated: April 10, 2026
Quick Overview
Given a binary tree, implement a function to traverse the tree in-order without using recursion. The function should take the root node of the tree as input and return a list of node values in the order they are visited.
Meta
April 10, 202613
12
2,244 solved
Given a binary tree, implement a function to traverse the tree in-order without using recursion. The function should take the root node of the tree as input and return a list of node values in the order they are visited.
This coding problem is frequently asked during Take-home Project at Meta. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Meta expects candidates to write production-quality code, not just solve the puzzle.
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
- Can you optimize the space complexity of your solution?
- How would you modify your solution to handle streaming input?
- Can you solve this iteratively instead of recursively (or vice versa)?
- How would you parallelize this solution?
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Problem Analysis
The problem requires us to traverse a binary tree in an in-order fashion without using recursion. The in-order traversal visits nodes in the left subtree, then the current node, and finally the right ...
Approach
- Initialize an empty stack and a current node pointer starting at the root of the tree.
- While there are nodes to process (either the stack is not empty or the current node is not null):
- Trav...
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