rotation on Binary Tree
Last updated: October 28, 2025
Quick Overview
Given a binary tree, implement a function to rotate the tree to the right by 90 degrees. The rotation should modify the tree in place, and the function should return the new root of the rotated tree. The input will be the root node of the binary tree, and the output should be the root node of the rotated tree.
ServiceNow
October 28, 20255
14
2,250 solved
Given a binary tree, implement a function to rotate the tree to the right by 90 degrees. The rotation should modify the tree in place, and the function should return the new root of the rotated tree. The input will be the root node of the binary tree, and the output should be the root node of the rotated tree.
This coding problem is frequently asked during Technical Screen at ServiceNow. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. ServiceNow expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
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 you test this solution thoroughly?
- How would your solution change if the input was sorted?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To rotate a binary tree to the right by 90 degrees, we need to understand the structure of the tree and how the nodes relate to each other. The right rotation requires the left subtree of the root nod...
Approach
- Identify the new root: The new root after a right rotation will be the left child of the current root.
- Reassign pointers: The right child of the new root (left child of the current roo...
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