class Solution(object):
    def findKthToTail(self, pListHead, k):
        if not pListHead:
            return None

        slow, fast = pListHead, pListHead
        for _ in range(k):
            if fast:
                fast = fast.next
            else:
                return None

        while fast:
            fast = fast.next
            slow = slow.next
        return slow