https://leetcode-cn.com/problems/kth-node-from-end-of-list-lcci/

    1. /**
    2.  * Definition for singly-linked list.
    3.  * public class ListNode {
    4.  *     int val;
    5.  *     ListNode next;
    6.  *     ListNode(int x) { val = x; }
    7.  * }
    8.  */
    9. class Solution {
    10.     public int kthToLast(ListNode head, int k) {
    11.         ListNode p=head, pre = head;
    12.         while(k-- > 0){
    13.             p=p.next;
    14.         }
    15.         while(p != null){
    16.             pre = pre.next;
    17.             p=p.next;
    18.         }
    19.         return pre.val;
    21.     }
    22. }