# HackerRank Solutions – Linked Lists – Detect a Cycle – Java Solution

All credits to Rodney Shaghoulian for this simple solution for the HackerRank challenge – Linked Lists – Detect a Cycle. This solution is written in Java.

// Author: Rodney Shaghoulian // Github: github.com/RodneyShag // Algorithm // // 1. Create a pointer that moves 1 step at a time: 'slow' // 2. Create a pointer that moves 2 steps at a time: 'fast' // 3. If the Linked List has a cycle, 'slow' and 'fast' will collide. /* A Node is defined as: class Node { int data; Node next; } */ // If "slow" and "fast" collide, we must have a cycle boolean hasCycle(Node head) { if (head == null) { return false; } Node slow = head; // moves 1 Node at a time Node fast = head; // moves 2 Nodes at a time while (fast != null && fast.next != null) { slow = slow.next; fast = fast.next.next; if (slow == fast) { return true; // since "slow" and "fast" collided } } return false; } // Time Complexity: O(n) // Space Complexity: O(1)