DFS on binary tree
Last updated: June 9, 2026
Quick Overview
Implement a Depth-First Search (DFS) algorithm to traverse a binary tree. Given the root node of a binary tree, return a list of values representing the nodes visited in preorder traversal (root, left, right). Your solution should handle trees of varying sizes and structures.
Splunk
June 9, 202631
4
2,446 solved
Implement a Depth-First Search (DFS) algorithm to traverse a binary tree. Given the root node of a binary tree, return a list of values representing the nodes visited in preorder traversal (root, left, right). Your solution should handle trees of varying sizes and structures.
Splunk uses this problem in the Onsite 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
- 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
- How would you parallelize this solution?
- What is the worst-case input for your solution?
- What if the input doesn't fit in memory?
- How would you test this solution thoroughly?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to perform a Depth-First Search (DFS) traversal on a binary tree, specifically in preorder format (root, left, right). This traversal can be efficiently implemented using recur...
Approach
- Base Case: If the current node is null, return an empty list. This handles leaf nodes and prevents further recursion.
- Recursive Case: Start with the current node's value.
- Call the DF...
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