flattening on Binary Tree
Last updated: July 4, 2025
Quick Overview
Perform a flattening on a binary tree and return the result.
Amazon
Coding & Algorithms
Software Engineer
Amazon
July 4, 2025Software Engineer
Phone Screen
Coding & Algorithms
Hard
142
12
3,989 solved
Perform a flattening on a binary tree and return the result.
Amazon 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
- 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
Tree structures and recursion
Data structure selection and trade-offs
Hash maps and frequency counting
Time and space complexity analysis
Common algorithm patterns (sliding window, two pointers, BFS/DFS)
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?
- How would your solution change if the input was sorted?
- How would you test this solution thoroughly?
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Practice DSA ProblemsSample Answer
Problem Analysis
To flatten a binary tree, we need to transform it into a linked list where each node's right pointer points to the next node in the pre-order traversal of the tree. This problem is best approached usi...
Approach
- Define a recursive function that takes the current node as an argument.
- If the current node is null, return.
- Recursively flatten the left subtree.
- Recursively flatten the right subtree....
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