Merge Three Sorted grids
Last updated: November 14, 2025
Quick Overview
Given three sorted linked lists, merge them into a single sorted result.
Vercel
Coding & Algorithms
Software Engineer
Vercel
November 14, 2025Software Engineer
Technical Screen
Coding & Algorithms
Medium
68
12
4,416 solved
Given three sorted linked lists, merge them into a single sorted result.
Coding interviews at Vercel 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
- 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
Graph algorithms and traversal
Common algorithm patterns (sliding window, two pointers, BFS/DFS)
Time and space complexity analysis
Data structure selection and trade-offs
Tree structures and recursion
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 is the worst-case input for your solution?
- How would you test this solution thoroughly?
- What if the input doesn't fit in memory?
- What happens if the input contains duplicates?
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Practice DSA ProblemsSample Answer
Problem Analysis
To merge three sorted linked lists, we can recognize that this problem is best approached using the two pointers technique. Each linked list can be traversed with a pointer, and we can compare the...
Approach
- Initialize three pointers, one for each linked list. Let’s call them
p1,p2, andp3, pointing to the head of each linked list respectively. - Create a new dummy node to help build the merged...
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