inversion on Binary Tree
Last updated: March 27, 2026
Quick Overview
Given a binary tree, write a function to invert the tree, meaning that for every node, its left and right children are swapped. The function should take the root of the binary tree as input and return the root of the inverted binary tree.
Redfin
March 27, 2026231
14
170 solved
Given a binary tree, write a function to invert the tree, meaning that for every node, its left and right children are swapped. The function should take the root of the binary tree as input and return the root of the inverted binary tree.
Redfin uses this problem in the Technical Screen 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 your solution change if the input was sorted?
- What is the worst-case input for your solution?
- How would you parallelize this solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Problem Analysis
To solve the problem of inverting a binary tree, we can recognize that it has a recursive structure. Specifically, for each node in the tree, we need to swap its left and right children, and then recu...
Approach
- Base Case: If the current node is null, return null. This handles the termination condition for our recursion.
- Swap Children: Swap the left and right children of the current node.
- **R...
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