0019.删除链表的倒数第 N 个结点

[0019.删除链表的倒数第 N 个结点](https://leetcode.cn/problems/remove-nth-node-from-end-of-list/

方法一：遍历

时间复杂度 $O(n)$，空间复杂度 $O(1)$。

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func removeNthFromEnd(head *ListNode, n int) *ListNode {
	dummy := &ListNode{Next: head}
	pre, now := dummy, dummy
	for ; n > 0; n-- {
		now = now.Next
	}

	for now.Next != nil {
		pre, now = pre.Next, now.Next
	}
	pre.Next = pre.Next.Next
	return dummy.Next
}