链表中倒数第k个结点

#思路：遍历整个链表，把链表中的元素放在列表中，索引第n-k个元素

class Node():
    def __init__(self,data):
        self.data = data
        self.next = None

class singleList():
    def __init__(self):
        self._head = None
    # 尾插法建立列表
    def append(self,data):
        if self._head == None:
            s = Node(data)
            self._head = s
        else:
            p =self._head
            while p.next !=None:
                p=p.next
            s= Node(data)
            p.next = s
    def countlength(self):
        p = self._head
        count = 0
        while p!= None:
            count += 1
            p= p.next
        return count

    def findk(self,k,count):
        res = []
        if k > count:
            return -1
        else:
            p = self._head
            while p!=None:
                # print(p.data)
                res.append(p.data)
                p = p.next
            return res[count-k]

slist = singleList()
data = int(input("请输入链表list1中的值，输入-1结束："))
while data!=-1:
    slist.append(data)
    data = int(input("请输入链表list1中的值，输入-1结束："))
count = slist.countlength()

print(slist.findk(2, count))