traversal on Binary Tree
Last updated: December 18, 2025
Quick Overview
Given a binary tree, implement a function to perform a traversal of the tree in a specified order (e.g., in-order, pre-order, or post-order) and return the values of the nodes as a list. The function should take the root node of the binary tree as input and output a list of integers representing the node values in the order they were traversed.
Datadog
December 18, 202536
15
688 solved
Given a binary tree, implement a function to perform a traversal of the tree in a specified order (e.g., in-order, pre-order, or post-order) and return the values of the nodes as a list. The function should take the root node of the binary tree as input and output a list of integers representing the node values in the order they were traversed.
This coding problem is frequently asked during Onsite at Datadog. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Datadog expects candidates to write production-quality code, not just solve the puzzle.
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
- Can you solve this iteratively instead of recursively (or vice versa)?
- Can you solve this in a single pass?
- 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 traverse a binary tree and return the values of the nodes in a specified order (in-order, pre-order, or post-order). This type of problem is well-suited for Depth-First Sear...
Approach
- Select the Traversal Method: Let's choose in-order traversal for this example.
- Define the Recursive Function: Create a helper function that takes a node as an argument and a list to sto...
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