题解 | #删除链表的倒数第n个节点#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head ListNode类
     * @param n int整型
     * @return ListNode类
     */
    public ListNode removeNthFromEnd (ListNode head, int n) {
        // write code here
        if (head == null || n <= 0) {
            return null;
        }

        ListNode fast = head;
        ListNode slow = head;

        for (int i = 0; i < n; i++) {
            if (fast == null) {
                return null;
            }
            fast = fast.next;
        }

        ListNode pre = null;
        while (fast != null) {
            pre = slow;
            slow = slow.next;
            fast = fast.next;
        }

        if (pre == null) {
            return slow.next;
        }
        pre.next  = pre.next.next;
        return head;
    }
}