Sword finger offer 22. the penultimate node in the linked list

Title Description

Problem analysis

Use the speed pointer and double pointer to do , Last but not least K It means that the fast and slow pointers are separated k Units to traverse
First, let the pointer go K A unit of ,while Loop through the fast pointer
Then let the slow pointer and the fast pointer go back together , Side by side while loop , Walking speed pointer .

（ The title of the linked list is mostly to use while loop ）

Code instance

/** * 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 fast = head;
        ListNode slow = head;
        while(fast != null&& k > 0){
    
            fast = fast.next;
            k--;
        }
        while(fast != null){
    
            fast = fast.next;
            slow = slow.next;
        }
        return slow;
    }
}