查找和删除倒数第n个节点的问题

class ListNode
{
    int val;
    ListNode next;
    ListNode(int x)
    {
        val = x;
    }
}
public class NthNodeFromEnd {
     public ListNode removeNthFromEnd(ListNode head, int n) 
     {
         ListNode p = head;
         ListNode q = head;
         for(int i = 0; i < n ; i++)
         {
             p = p.next;
         }
         if(p == null)//如果p==null，说明倒数第n个就是第一个节点，即头结点。
         {
             head = head.next;
             return head;
         }
         while(p.next != null)
         {
             p = p.next;
             q = q.next;
         }
         if(q.next != null)
         {
             q.next = q.next.next;
         }
         
         return head;
     }
     public ListNode removeNthFromEnd2(ListNode head, int n) 
     {
        //因为要删掉倒数第n个节点，那就必须找到倒数第n+1个节点
        //如果倒数第n正好是头结点，那么头结点前面没有节点了很麻烦，我们可以设置一个节点作为头结点之前的节点
        //设置一个头结点，这样就不用单独对原始头结点处理了
         ListNode dumy = new ListNode(0);
         dumy.next = head;
         ListNode p = dumy;
         ListNode q = dumy;
         for(int i = 0; i < n; i ++)
         {
             p = p.next;
         }
         while(p.next!=null)
         {
             p = p.next;
             q = q.next;
         }
         q.next = q.next.next;
         return dumy.next;
     }
     //找倒数第n个节点
     public ListNode findNthFromEnd(ListNode head, int n)
     {
         ListNode p = head;
         ListNode q = head;
         for(int i = 0; i < n-1; i ++)
         {
             p = p.next;
         }
         while(p.next!=null)
         {
             p = p.next;
             q = q.next;
         }
         return q;
     }
     
     public static void main(String[] args)
     {
         NthNodeFromEnd rn = new NthNodeFromEnd();
         ListNode n1 = new ListNode(1);
         ListNode n = rn.removeNthFromEnd(n1, 1);
         System.out.println(rn.findNthFromEnd(n1, 1).val);
         if(n == null)
         {
             System.out.println(n);
         }
         while(n!= null)
         {
             System.out.println(n.val);
             n = n.next;
         }
     }
}