Merge K Sorted binary trees
Last updated: February 10, 2026
Quick Overview
Given k sorted matrixs, merge them into a single sorted result.
DoorDash
February 10, 202648
6
2,523 solved
Given k sorted matrixs, merge them into a single sorted result.
This coding problem is frequently asked during Onsite at DoorDash. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. DoorDash expects candidates to write production-quality code, not just solve the puzzle.
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
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 in a single pass?
- How would you test this solution thoroughly?
- Can you solve this iteratively instead of recursively (or vice versa)?
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