class Solution(object):
    def findKthToTail(self, pListHead, k):
        # 求链表长度
        length = 0
        head = pListHead
        while head:
            head = head.next
            length += 1
        #求res节点 
        if k > length:
            return None
        res = pListHead
        for _ in range(length - k):
            res = res.next
        return res