Optimize inversion for O(1) space
Last updated: September 13, 2025
Quick Overview
Given a binary tree, write a function to invert the tree in place, ensuring that the solution uses O(1) space. The function should take the root node of the binary tree as input and return the root of the inverted tree.
OpenAI
September 13, 2025339
5
3,207 solved
Given a binary tree, write a function to invert the tree in place, ensuring that the solution uses O(1) space. The function should take the root node of the binary tree as input and return the root of the inverted tree.
OpenAI uses this problem in the Phone 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
- 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
- What happens if the input contains duplicates?
- How would you modify your solution to handle streaming input?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
To invert a binary tree, we need to swap the left and right children of all nodes in the tree. This problem can effectively be solved using a recursive approach or an iterative approach with a stack. ...
Approach
- Start with the root node of the binary tree. If the root is None, return None immediately as the tree is empty.
- Initialize a queue (using a list) and enqueue the root node.
- While the queue is...
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