Can you describe how to detect a cycle in a linked list efficiently?
Direct Answer
This question tests the implementation of Floyd's Cycle-Finding Algorithm. It evaluates knowledge of fast and slow pointer techniques.
Why Interviewers Ask This
Cycle detection is a fundamental problem in linked list manipulation. Interviewers ask this to ensure candidates know the standard O(n) time and O(1) space solution. It distinguishes those who memorize solutions from those who understand the underlying pointer mechanics and can adapt them.
How to Answer This Question
Introduce the two-pointer approach where one pointer moves twice as fast as the other. Explain that if a cycle exists, the fast pointer will eventually meet the slow pointer inside the loop. Discuss what happens if the fast pointer reaches the end (no cycle). Mention how to find the start of the cycle if required.
Key Points to Cover
- Two pointers: slow and fast
- Fast moves 2x speed of slow
- Meeting point indicates cycle
- O(n) time, O(1) space
Sample Answer
I would use Floyd's Tortoise and Hare algorithm with two pointers, slow and fast. The slow pointer advances one node at a time, while the fast pointer advances two nodes. If there is no cycle, the fast pointer will reach…
Common Mistakes to Avoid
- Infinite loops due to incorrect pointer updates
- Not handling null references properly
- Using extra space for visited nodes
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