带头结点。
public ListNode removeNthFromEnd(ListNode head, int n) {
ListNode first = head , seconde = head ;
for(int i = 1 ; i <= n ; i++) first = first.next ;
if(first == null) return head.next ;
first = first.next ;
while(first != null){
first = first.next ;
seconde = seconde.next ;
}
seconde.next = seconde.next.next ;
return head ;
}