flattening on Binary Tree
Last updated: August 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 modified tree where each node's left child is set to null and the right child points to the next node in the flattened list.
Expedia
August 28, 2025179
10
4,387 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 modified tree where each node's left child is set to null and the right child points to the next node in the flattened list.
Coding interviews at Expedia 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
- 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
- Can you solve this iteratively instead of recursively (or vice versa)?
- Can you optimize the space complexity of your solution?
- How would you test this solution thoroughly?
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Problem Analysis
To solve the problem of flattening a binary tree into a linked list in pre-order traversal order, we can utilize the Depth-First Search (DFS) pattern. This approach is optimal as it allows us to v...
Approach
- Define a recursive function that accepts a node as input. This function will perform the flattening process.
- Base Case: If the current node is null, return immediately.
- **Recursiv...
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