如何判斷單向連結清單有環

有一個單向連結清單，連結清單中可能出現“環”，那麼，如何用程式來判斷該連結清單是否為有環連結清單呢？

/**
 * @Author: subd
 * @Date: 2019/9/4 7:02
 */
public class SingleLinkNode {
    /**
     * 連結清單節點
     */
    private static class Node {
        int data;
        Node next;

        public Node(int data) {
            this.data = data;
        }
    }

    /**
     * 判斷是否有環
     *
     * @param head 連結清單頭結點
     * @return
     */
    public static boolean isCycle(Node head) {
        Node p1 = head;
        Node p2 = head;
        int step = 0;
        while (p2 != null && p2.next != null) {
            p1 = p1.next;
            p2 = p2.next.next;
            if (p1 == p2) {
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {
        Node node1 = new Node(5);
        Node node2 = new Node(3);
        Node node3 = new Node(2);
        Node node4 = new Node(7);
        Node node5 = new Node(6);
        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = node5;
        node5.next = node2;
        System.out.println(isCycle(node1));
    }
}