Sword finger offer 22 The penultimate node in the linked list

difficulty ： Simple
The frequency of ：81
subject ： Enter a linked list , Output the last number in the list k Nodes . In order to conform to the habits of most people , From 1 Start counting , That is, the tail node of the list is the last 1 Nodes .

for example , A list has 6 Nodes , Start from the beginning , Their values, in turn, are 1、2、3、4、5、6. The last of the list 3 Each node has a value of 4 The node of .

Their thinking ： Speed pointer

Be careful ：

• while（p1!=null）, Here is p1, instead of p1.next
  Code ：

/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */
class Solution {
    
    public ListNode getKthFromEnd(ListNode head, int k) {
    
        ListNode p1=head;
        ListNode p2=head;
        while(k>0){
    
            p1=p1.next;
            k--;
        }
        while(p1!=null){
    
            p1=p1.next;
            p2=p2.next;
        }
        return p2;
    }
}