import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 
     * @param n int整型 
     * @return ListNode类
     */
    public ListNode removeNthFromEnd (ListNode head, int n) {
        // write code here
        ListNode fast = head;
        ListNode slow = head;
        
        for (int i = 0; i < n; i++) {
            fast = fast.next;
        }
        // 如果 n 的值等于链表长度 即删除的是第一个
        if (fast == null) {    
            return head.next;
        }
        
        // 如果删除的不是第一个
        while (fast.next != null) {
            slow = slow.next;
            fast = fast.next;
        }
        slow.next = slow.next.next;
        return head;
    }
}