Linked List Cycle
Given the head of a linked list, determine if the linked list contains a cycle.
A cycle exists if there is some node in the list that can be reached again by continuously following the next pointer.
Return true if there is a cycle in the linked list. Otherwise, return false.
Example 1
Input
4 3 2 0 -4 1
Output
true
Explanation
The last node points back to the node at index 1, creating a cycle.
Example 2
Input
2 1 2 -1
Output
false
Explanation
The last node points to null, so the linked list does not contain a cycle.
Constraints
Hints:
Hint 1
Try using two pointers moving through the linked list at different speeds.
Hint 2
Use a slow pointer that moves one step at a time and a fast pointer that moves two steps at a time.
Author & Technical Reviewer
Technically reviewed by: ExamAdda Technical Review Team
Technical Reviewers, ExamAdda
Software engineers at ExamAdda who check every article's definitions, complexity claims and code examples before and after publishing.
Published
Aug 10, 2026
Last updated
Aug 10, 2026
Content Verification Methodology
Definitions and complexity claims were checked against authoritative computer-science references. Code examples were compiled and tested with standard, boundary and edge-case inputs.
Expected Output