LeetCode题 19. 删除链表的倒数第 N 个结点(双指针法)

给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。

示例 1：

输入：head = [1,2,3,4,5], n = 2
输出：[1,2,3,5]
示例 2：

输入：head = [1], n = 1
输出：[]
示例 3：

输入：head = [1,2], n = 1
输出：[1]

提示：

链表中结点的数目为 sz
1 <= sz <= 30
0 <= Node.val <= 100
1 <= n <= sz

进阶：你能尝试使用一趟扫描实现吗？

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode pre = new ListNode(-1);
        pre.next = head;

        ListNode slow = pre;
        ListNode fast = pre;

        while(n-- > 0){
            fast = fast.next;
        }

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

        }

        temp.next = slow.next;
        return pre.next;
       
        

    }
}