inversion on Binary Tree
Last updated: June 10, 2026
Quick Overview
Given a binary tree, write a function to invert the tree, which means swapping the left and right children of all nodes in the tree. The function should take the root node of the binary tree as input and return the root of the inverted tree.
PayPal
June 10, 202632
13
4,666 solved
Given a binary tree, write a function to invert the tree, which means swapping the left and right children of all nodes in the tree. The function should take the root node of the binary tree as input and return the root of the inverted tree.
Coding interviews at PayPal 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
- How would your solution change if the input was sorted?
- What happens if the input contains duplicates?
- How would you modify your solution to handle streaming input?
- What if the input doesn't fit in memory?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of inverting a binary tree, we can identify that this is a classic tree traversal problem. The specific pattern we will use is Depth-First Search (DFS), which can be implement...
Approach
- Base Case: If the current node is
None, returnNone. This handles empty trees or when we've reached the end of a branch. - Swap: For the current node, swap its left and right childre...
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