快慢指针
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
def kthToLast(self, head: ListNode, k: int) -> int:
fast = head
slow = head
while k - 1 > 0:
fast = fast.next
k-=1
while fast.next != None:
fast = fast.next
slow = slow.next
return slow.val