1.     public ListNode reverseList(ListNode head) {
    2.         ListNode pre = null;
    3.         while (head != null) {
    4.             ListNode next = head.next;
    5.             // 当前节点的子节点指向前一个节点
    6.             head.next = pre;
    7.             // 向前移动
    8.             pre = head;
    9.             head = next;
    10.         }
    11.         return pre;
    12.     }
    1.  public ListNode reverseList(ListNode head) {
    2.         ListNode pre = null;
    3.         for (pre = null; head != null;) {
    4.             ListNode next = head.next;
    5.             head.next = pre;
    6.             pre = head;
    7.             head = next;
    8.         }
    9.         return pre;
    10.     }