Merge Three Sorted matrixs
Last updated: November 17, 2025
Quick Overview
Given k sorted grids, merge them into a single sorted result.
Scale AI
November 17, 202530
7
1,471 solved
Given k sorted grids, merge them into a single sorted result.
Scale AI uses this problem in the Technical 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
- 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
- What if the input doesn't fit in memory?
- What is the worst-case input for your solution?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
We need to merge k sorted matrices, which can be considered as a multi-way merge problem. The most suitable pattern here is the use of a min-heap (priority queue). The reason is that we want to ef...
Approach
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Initialize a min-heap: Start by adding the first element of each matrix into the heap along with its matrix index and element index for tracking.
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Extract and merge: While the heap is...
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