LinkedListCycleDetection.txt

class ListNode {
    int val;
    ListNode next;

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

public class LinkedListCycleDetection {
    public boolean hasCycle(ListNode head) {
        if (head == null || head.next == null) {
            return false; // No cycle if the list is empty or has only one node.
        }

        ListNode slow = head;
        ListNode fast = head;

        while (fast != null && fast.next != null) {
            slow = slow.next; // Move one step at a time.
            fast = fast.next.next; // Move two steps at a time.

            if (slow == fast) {
                return true; // If there's a cycle, the two pointers will meet.
            }
        }

        return false; // If we reach the end of the list, there's no cycle.
    }

    public static void main(String[] args) {
        LinkedListCycleDetection cycleDetection = new LinkedListCycleDetection();
        ListNode head = new ListNode(3);
        ListNode node2 = new ListNode(2);
        ListNode node0 = new ListNode(0);
        ListNode node4 = new ListNode(4);

        head.next = node2;
        node2.next = node0;
        node0.next = node4;
        node4.next = node2; // Creating a cycle

        boolean hasCycle = cycleDetection.hasCycle(head);
        System.out.println("Does the linked list have a cycle? " + hasCycle);
    }
}