Merge Two Sorted linked lists
Last updated: August 7, 2025
Quick Overview
Given two sorted linked lists, merge them into a single sorted linked list. The merged linked list should maintain the order of elements from both input lists. Your solution should return the head of the newly merged linked list.
Twitter/X
August 7, 2025237
5
3,692 solved
Given two sorted linked lists, merge them into a single sorted linked list. The merged linked list should maintain the order of elements from both input lists. Your solution should return the head of the newly merged linked list.
This coding problem is frequently asked during Onsite at Twitter/X. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Twitter/X expects candidates to write production-quality code, not just solve the puzzle.
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
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?
- How would you parallelize this solution?
- What if the input doesn't fit in memory?
- How would your solution change if the input was sorted?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we need to merge two sorted linked lists into a single sorted linked list. The key pattern to apply here is the 'Two Pointers' technique. This technique is suitable because we can tra...
Approach
We will use the following step-by-step algorithm:
- Initialize a dummy node to act as the head of the merged list and a pointer to the current position in the merged list.
- Use two pointers, one fo...
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