Merge K Sorted grids
Last updated: August 9, 2025
Quick Overview
Given three sorted matrixs, merge them into a single sorted result.
PayPal
Coding & Algorithms
Software Engineer
PayPal
August 9, 2025Software Engineer
Take-home Project
Coding & Algorithms
Easy
131
14
3,204 solved
Given three sorted matrixs, merge them into a single sorted result.
PayPal uses this problem in the Take-home Project 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
- 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
Time and space complexity analysis
Hash maps and frequency counting
Sorting and searching
Common algorithm patterns (sliding window, two pointers, BFS/DFS)
Dynamic programming and memoization
Edge cases and input validation
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 you parallelize this solution?
- What if the input doesn't fit in memory?
- 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 merge three sorted matrices into a single sorted result, we can leverage the min-heap (priority queue) data structure. This approach is suitable because it allows us to efficiently access the s...
Approach
- Initialize a min-heap: Start with an empty min-heap.
- Insert Elements: Insert the first element of each of the three matrices into the min-heap. Since the matrices are sorted, the first e...
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