flattening on Binary Tree
Last updated: March 25, 2026
Quick Overview
Perform a flattening on a binary tree and return the result.
Uber
Coding & Algorithms
Software Engineer
Uber
March 25, 2026Software Engineer
Technical Screen
Coding & Algorithms
Medium
53
4
575 solved
Perform a flattening on a binary tree and return the result.
Coding interviews at Uber 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
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
Binary search and divide and conquer
Dynamic programming and memoization
Tree structures and recursion
Sorting and searching
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
- How would your solution change if the input was sorted?
- How would you parallelize this solution?
- How would you test this solution thoroughly?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
To flatten a binary tree means to convert it into a linked list in place. The key observation is that we can use a depth-first search (DFS) approach to traverse the binary tree and rearrange the nodes...
Approach
- Initialize: Create a pointer to keep track of the last processed node during the traversal.
- Post-order Traversal: Start from the root, recursively flatten the left subtree followed by t...
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