inversion on Binary Tree
Last updated: April 17, 2026
Quick Overview
Given a binary tree, write a function to invert the tree, swapping the left and right children of all nodes. The function should take the root of the binary tree as input and return the root of the inverted tree. For example, if the input tree is [4, 2, 7, 1, 3, 6, 9], the output should be [4, 7, 2, 9, 6, 3, 1].
Doordash
April 17, 20263
5
4,975 solved
Given a binary tree, write a function to invert the tree, swapping the left and right children of all nodes. The function should take the root of the binary tree as input and return the root of the inverted tree. For example, if the input tree is [4, 2, 7, 1, 3, 6, 9], the output should be [4, 7, 2, 9, 6, 3, 1].
Doordash uses this problem in the Take-home Project 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 if the input doesn't fit in memory?
- What is the worst-case input for your solution?
- Can you optimize the space complexity of your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to invert a binary tree, which means swapping the left and right children of all nodes. This can be effectively approached using Depth-First Search (DFS) or Breadth-First Searc...
Approach
- Base Case: If the current node is
None, returnNone. This handles empty subtrees. - Swap Children: For the current node, swap its left and right children.
- Recursive Calls: Recur...
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