DFS on binary tree
Last updated: March 11, 2026
Quick Overview
Implement a Depth-First Search (DFS) algorithm to traverse a binary tree. Given the root node of a binary tree, return the values of the nodes in a specific order (e.g., pre-order, in-order, or post-order). Your solution should handle edge cases, such as an empty tree, and return the result as a list of integers.
SpaceX
March 11, 20260
14
4,771 solved
Implement a Depth-First Search (DFS) algorithm to traverse a binary tree. Given the root node of a binary tree, return the values of the nodes in a specific order (e.g., pre-order, in-order, or post-order). Your solution should handle edge cases, such as an empty tree, and return the result as a list of integers.
Coding interviews at SpaceX 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
- 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 modify your solution to handle streaming input?
- How would your solution change if the input was sorted?
- How would you test this solution thoroughly?
- What if the input doesn't fit in memory?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to traverse a binary tree using Depth-First Search (DFS). The pattern that applies here is a tree traversal method where we explore as far as possible along each branch before ...
Approach
- Define the Tree Structure: We will define a class for the tree node with properties for the value, left child, and right child.
- Base Case: If the root is
None, return an empty list. ...
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