Merge Three Sorted strings
Last updated: October 10, 2025
Quick Overview
Given k sorted grids, merge them into a single sorted result.
Apple
October 10, 2025595
3
3,128 solved
Given k sorted grids, merge them into a single sorted result.
This coding problem is frequently asked during Take-home Project at Apple. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Apple 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
- How would you test this solution thoroughly?
- Can you optimize the space complexity of your solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem of merging k sorted grids can be efficiently solved using a min-heap (or priority queue) data structure. The reason this approach is optimal here is that it allows us to efficiently ac...
Approach
- Initialize a min-heap: Start with an empty min-heap.
- Insert the first element of each grid: For each of the k sorted grids, insert the first element along with its grid index and elemen...
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