var getKthFromEnd = function(head, k) {
let fast = head, slow = head;
while (fast && k > 0) {
[fast, k] = [fast.next, k - 1];
}
while (fast) {
[fast, slow] = [fast.next, slow.next];
}
return slow;
};
https://leetcode-cn.com/problems/lian-biao-zhong-dao-shu-di-kge-jie-dian-lcof/