DFS on binary tree
Last updated: March 12, 2026
Quick Overview
Implement a depth-first search (DFS) algorithm to traverse a binary tree. Given the root of a binary tree, return the values of the nodes in the order they are visited during the DFS traversal. Your solution should handle edge cases, such as an empty tree, and output the result as a list of node values.
Meta
March 12, 20263
12
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Implement a depth-first search (DFS) algorithm to traverse a binary tree. Given the root of a binary tree, return the values of the nodes in the order they are visited during the DFS traversal. Your solution should handle edge cases, such as an empty tree, and output the result as a list of node values.
Meta uses this problem in the Take-home Project 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?
- What if the input doesn't fit in memory?
- How would you parallelize this solution?
- How would you modify your solution to handle streaming input?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we need to implement a Depth-First Search (DFS) algorithm to traverse a binary tree. DFS is particularly suited for tree traversal as it explores as far down a branch as possible befo...
Approach
- Base Case: If the root is
None, return an empty list because there are no nodes to traverse. - Recursive Case: Initialize a result list to store the node values.
- Visit the root node...
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