题目：

题解：

func removeNthFromEnd(head *ListNode, n int) *ListNode {
    dummy := &ListNode{0, head}
    first, second := head, dummy
    for i := 0; i < n; i++ {
        first = first.Next
    }
    for ; first != nil; first = first.Next {
        second = second.Next
    }
    second.Next = second.Next.Next
    return dummy.Next
}