DetectCycleInLL.md

package com.thealgorithms.linkedlist;

class ListNode { int val; ListNode next; ListNode(int val) { this.val = val; this.next = null; } }

public class DetectCycle {

public static boolean hasCycle(ListNode head) {
    ListNode slow = head, fast = head;
    while (fast != null && fast.next != null) {
        slow = slow.next;
        fast = fast.next.next;
        if (slow == fast) {
            return true; // cycle detected
        }
    }
    return false; // no cycle
}

public static void main(String[] args) {
    ListNode head = new ListNode(3);
    head.next = new ListNode(2);
    head.next.next = new ListNode(0);
    head.next.next.next = new ListNode(-4);
    head.next.next.next.next = head.next; // create a cycle

    System.out.println("Cycle exists: " + hasCycle(head));
}

}