双指针-单链表反转

    static class Node {
        private Node next;
        private int val;

        public Node(Node next, int val) {
            this.next = next;
            this.val = val;
        }
    }

    public static void main(String[] args) {

        Node nodeA = new Node(null, 1);
        Node nodeB = new Node(nodeA, 2);
        Node nodeC = new Node(nodeB, 3);
        Node nodeD = new Node(nodeC, 4);
        Node header = new Node(nodeD, 5);

        Node pre = null;
        Node cur = header;
        Node next = cur.next;
        while (cur.next != null) {
            cur.next = pre;
            pre = cur;
            cur = next;
            next = cur.next;
        }
        cur.next = pre;

        while (cur != null) {
            System.out.println(cur.val);
            cur = cur.next;
        }
}