08删除链表的倒数第n个节点

删除链表的倒数第n个节点

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

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;
  }
}

public ListNode removeNthFromEnd(ListNode head, int n) {
  ListNode dummy = new ListNode(0,head);
  ListNode first = head;
  ListNode second = dummy;
  for (int i = 0; i < n; i++) {
    first = first.next;
  }

  while (first!=null){
    first = first.next;
    second = second.next;
  }

  second.next = second.next.next;
  return dummy.next;

}