/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        int len=0;
        ListNode p = head;
        while(p!=null){
            len++;
            p=p.next;
        }
        int target = len - n;
        if(target<0){
            return null;
        }else if(target==0){
            head = head.next;
        }else{
            ListNode q = null;
            p=head;
            int count = 0;
            while(count<len-n){
                q=p;
                p=p.next;
                count++;
            }
            q.next = p.next;
        }
        return head;
    }
}