Two Pointers on linked list
Last updated: August 7, 2025
Quick Overview
Given a singly linked list, implement the two-pointer technique to determine if there is a cycle in the list. Return true if a cycle exists, and false otherwise. Your solution should have a time complexity of O(n) and a space complexity of O(1).
Snapchat
August 7, 202536
7
3,340 solved
Given a singly linked list, implement the two-pointer technique to determine if there is a cycle in the list. Return true if a cycle exists, and false otherwise. Your solution should have a time complexity of O(n) and a space complexity of O(1).
Snapchat 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
- 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?
- How would you parallelize this solution?
- What if the input doesn't fit in memory?
- How would you test this solution thoroughly?
Sharpen Your Skills on Codemia
Practice similar problems with our interactive workspace, get AI feedback, and track your progress.
Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to determine if there is a cycle in a singly linked list. The two-pointer technique, specifically Floyd's Cycle Detection Algorithm (also known as the Tortoise and Hare algorit...
Approach
- Initialize two pointers:
slowandfast. Set both pointers to the head of the linked list. - Move the
slowpointer one step (i.e.,slow = slow.next) and thefastpointer two steps (i.e., ...
Submit Your Answer
