Merge Two Sorted linked lists
Last updated: February 2, 2026
Quick Overview
Given two sorted linked lists, merge them into a single sorted linked list. The resulting linked list should maintain the order of elements from both input lists. You should implement a function that takes the heads of the two linked lists as input and returns the head of the merged linked list.
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February 2, 202643
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2,204 solved
Given two sorted linked lists, merge them into a single sorted linked list. The resulting linked list should maintain the order of elements from both input lists. You should implement a function that takes the heads of the two linked lists as input and returns the head of the merged linked list.
Coding interviews at Discord 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
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 happens if the input contains duplicates?
- Can you solve this in a single pass?
- How would your solution change if the input was sorted?
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Problem Analysis
The problem requires merging two sorted linked lists into one sorted linked list. The key pattern that applies here is the two pointers technique. Since both input linked lists are already sorted,...
Approach
- Initialize a dummy node which will serve as the starting point of the merged linked list. This makes it easier to return the head of the merged list later.
- Create two pointers,
p1andp2, in...
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