flattening on Binary Tree
Last updated: July 28, 2025
Quick Overview
Given a binary tree, flatten it into a linked list in-place following the same order as a pre-order traversal. The output should be the head of the flattened linked list, where each node's left child is null and the right child points to the next node in the list.
Morgan Stanley
July 28, 2025462
7
2,143 solved
Given a binary tree, flatten it into a linked list in-place following the same order as a pre-order traversal. The output should be the head of the flattened linked list, where each node's left child is null and the right child points to the next node in the list.
This coding problem is frequently asked during Technical Screen at Morgan Stanley. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Morgan Stanley 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 your solution change if the input was sorted?
- What happens if the input contains duplicates?
- How would you modify your solution to handle streaming input?
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Practice DSA ProblemsSample Answer
Problem Analysis
To flatten a binary tree into a linked list in-place following pre-order traversal, we can utilize a recursive approach. The specific pattern that applies here is a pre-order traversal, where ...
Approach
Our approach involves a recursive function that will traverse the tree in pre-order and adjust the pointers accordingly. Here’s the step-by-step algorithm:
- Base Case: If the current node is nu...
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