DetectLoop.java

package java1.algorithms.linkedlist;

public class DetectLoop {
    private static boolean hasLoop(Node head) {
        Node slowPtr = head;
        Node fastPtr = head;

        while(fastPtr != null && fastPtr.next != null) {
            slowPtr = slowPtr.next;
            fastPtr = fastPtr.next.next;
            if(slowPtr == fastPtr) return true;
        }

        return false;
    }

    public static void main(String[] args) {
        Node headNode = new Node(10);
        Node node2 = new Node(20);
        Node node3 = new Node(30);
        Node node4 = new Node(40);
        Node node5 = new Node(50);
        Node node6 = new Node(60);
        Node node7 = new Node(70);
        Node node8 = new Node(80);

        headNode.setNext(node2);
        node2.setNext(node3);
        node3.setNext(node4);
        node4.setNext(node5);
        node5.setNext(node6);
        node6.setNext(node7);
        node7.setNext(node8);
        node8.setNext(headNode);

        System.out.println(hasLoop(headNode));
    }
}