traversal on Binary Tree
Last updated: February 17, 2026
Quick Overview
Given a binary tree, implement a function to perform a traversal (in-order, pre-order, or post-order) and return the values of the nodes in an array. Your function should take the root node of the binary tree as input and output an array of integers representing the order of traversal.
Capital One
February 17, 20266
3
609 solved
Given a binary tree, implement a function to perform a traversal (in-order, pre-order, or post-order) and return the values of the nodes in an array. Your function should take the root node of the binary tree as input and output an array of integers representing the order of traversal.
This coding problem is frequently asked during Technical Screen at Capital One. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Capital One 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
- How would you test this solution thoroughly?
- What is the worst-case input for your solution?
- Can you solve this in a single pass?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
This problem requires us to traverse a binary tree and return the node values in a specified order. The most common traversal methods for binary trees are in-order, pre-order, and post-order. Given th...
Approach
We will implement the recursive DFS algorithm for each traversal type. As an example, let's detail the in-order traversal:
- Base Case: If the current node is null, return an empty list.
- **Rec...
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