Optimize traversal for O(n) time
Last updated: December 26, 2025
Quick Overview
Given a binary tree, implement a traversal algorithm that visits each node in O(n) time. Your function should return the values of the nodes in the order they are visited as an array. Ensure your solution handles edge cases, such as an empty tree.
PlanetScale
December 26, 20253
9
2,661 solved
Given a binary tree, implement a traversal algorithm that visits each node in O(n) time. Your function should return the values of the nodes in the order they are visited as an array. Ensure your solution handles edge cases, such as an empty tree.
Coding interviews at PlanetScale 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
- 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 solve this iteratively instead of recursively (or vice versa)?
- How would your solution change if the input was sorted?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we are tasked with traversing a binary tree and returning the values of the nodes in the order they are visited. The most suitable patterns for this problem are Depth-First Search (DF...
Approach
We will implement a DFS traversal using recursion. The steps are as follows:
- Define a function that takes the root of the binary tree as input.
- Initialize an empty list to store the values of th...
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