Optimize inversion for O(1) space
Last updated: November 16, 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 tree as input and return the root of the inverted tree.
Zillow
November 16, 20252
14
1,667 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 tree as input and return the root of the inverted tree.
This coding problem is frequently asked during Take-home Project at Zillow. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Zillow expects candidates to write production-quality code, not just solve the puzzle.
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 is the worst-case input for your solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem involves inverting a binary tree in place, which means we need to swap the left and right children of every node. The specific pattern that applies here is Depth-First Search (DFS), as...
Approach
We will utilize a recursive approach to invert the binary tree. The steps are as follows:
- If the current node is null, return immediately (base case).
- Swap the left and right children of the cur...
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