剑指 Offer 22. 链表中倒数第k个节点

首先定义两个指针fast和slow都指向头节点，让fast指针先走，走过k个节点后再让slow走，当fast指针走到末尾的时候slow指针正好走到倒数第k个节点

 

var getKthFromEnd = function(head, k) {
   let fast = slow = head;
   while(fast) {
       fast = fast.next;
       if(k-- <= 0) {
           slow = slow.next;
       }
   }
   return slow;
};