swift创建链表三

删除链表中倒数第N个节点

enum MyError : Error {
        case error_0
        case error_1
    }
    func removeLastNode(_ head : Node , lastPosition : Int) throws{
        var firstNode = head
        var secondNode = head
        
        for _ in 0..<lastPosition {
            if secondNode.next == nil{
                throw MyError.error_0
            }else{
                secondNode = secondNode.next!
            }
        }
        while secondNode.next != nil {
            firstNode = firstNode.next!
            secondNode = secondNode.next!
        }
        firstNode.next = firstNode.next?.next
        
    }