How do you find the intersection point of two linked lists?
This problem tests cycle detection logic and pointer arithmetic in linked list scenarios.
Why Interviewers Ask This
Intersection problems appear in graph theory and memory layout debugging. It checks if you can solve problems without extra space (O(1) space solution). Efficiency is critical in high-frequency trading environments.
How to Answer This Question
Present the two-pointer technique where pointers traverse both lists simultaneously. Explain how resetting the pointer to the head of the other list after reaching the end aligns them at the intersection. Alternatively, mention calculating lengths and skipping the difference.
Key Points to Cover
- Two-pointer traversal method
- Resetting pointers to opposite heads
- Meeting point indicates intersection
- O(1) space complexity
Sample Answer
I would use two pointers starting at the heads of both lists. Traverse both; when a pointer reaches the end, redirect it to the other list's head. If they intersect, they will meet at the intersection node. If not, they will both become null at the same time. This ensures O(m+n) time and O(1) space.
Common Mistakes to Avoid
- Using a hash set leading to O(n) space
- Not handling the case where lists do not intersect
- Incorrectly calculating length differences
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