019.Remove Nth Node From End of List

//需要注意是删除掉头的特殊情况

public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode pointer1=head;
        ListNode pointer2=head;
        for(int i=0;i<n;i++){
            pointer1=pointer1.next;
        }
        if(pointer1==null)
        {head=head.next;
        return head ;
        }//删除掉头的特殊情况，这时你指针已经变成 null了
        while(pointer1.next!=null){
            pointer1=pointer1.next;
            pointer2=pointer2.next;
        }
        ListNode tmp=pointer2.next;
        pointer2.next=pointer2.next.next;
        tmp=null;
        return head;
}
}