单链表就地反转

 1     // 1.就地反转法
 2     public ListNode reverseList1(ListNode head) {
 3         if (head == null)
 4             return head;
 5         ListNode dummy = new ListNode(-1);
 6         dummy.next = head;
 7         ListNode prev = dummy.next;
 8         ListNode pCur = prev.next;
 9         while (pCur != null) {
10             prev.next = pCur.next;
11             pCur.next = dummy.next;
12             dummy.next = pCur;
13             pCur = prev.next;
14         }
15         return dummy.next;
16     }