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 class Solution {
    /**
     *
     * @param head ListNode类
     * @param n int整型
     * @return ListNode类
     */
    public ListNode removeNthFromEnd (ListNode head, int n) {
        if (head == null) return null;
        ListNode res = head;
        ArrayList<ListNode> list = new ArrayList<>();
        ListNode temp = head;
        ListNode q = null;
        while (temp != null) {
            ListNode node = new ListNode(temp.val);
            list.add(node);
            temp = temp.next;
        }
        int size = list.size();
        if (size < n) return null;
        for (int i = 0 ; i < size - n; i++) {
            q = head;
            head = head.next;
        }
        if (q == null) {
            q = head;
            head = head.next;
            q.next = null;
            return head;
        }
        ListNode next = head.next;
        head.next = null;
        q.next = next;
        return res;
    }
}