算法-----单链表逆序

while(head != null){
  next = head.next;
  head.next = pre;
  pre = head;
  head = next;  
}

Node cur = pre.next;
Node next1 = cur.next;
cur.next = pos;
Node next2 = null;

while(next1 != pos){
   next2 = next1.next;
   next1.next = cur;
   cur = next1;
   next1 = next2;
}