Linked Lists · Coding problem
Detect a Cycle in a Linked List
A free coding problem from the Singly Linked List Basics skill. Read it here, then solve it in the app in Java or Python.
- Easy
- Coding problem
- Free
- Java and Python
The problem
Given the head of a linked list, determine whether it contains a cycle - i.e. some node's next pointer eventually leads back to a node already visited, rather than to null.
Example
Input: 1 -> 2 -> 3 -> 4 -> (back to 2)
Output: true
Do it in O(1) extra space - don't use a HashSet to track visited nodes.
Constraints
0 <= number of nodes <= 2 * 10^5-10^5 <= node value <= 10^5
How it's graded
- Run checks your code against the examples. Submit also runs a hidden suite in four groups - basic cases, edge cases, random inputs and performance tests at the size limit - and shows which groups pass, never the hidden inputs.
- Stuck? Hints come in four steps, from a nudge to a code skeleton, each costing part of the points.
- Once you pass, you see the approaches from brute force to optimal, and where your solution lands among them.
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