输入一个链表，找到倒数第K个节点。使得只扫描一次链表。

package com.mytest.mymain;

class ListNode {
int val;
ListNode next = null;

ListNode(int val) {
this.val = val;
}
}

public class FindKthtotail {
public static void main(String[] args) {
FindKthtotail findKthtotail=new FindKthtotail();
ListNode One =new ListNode(2);
ListNode Two =new ListNode(3);
ListNode Third =new ListNode(4);
ListNode Four =new ListNode(5);
ListNode Five =new ListNode(6);
One.next=Two;
Two.next= Third;
Third.next=Four;
Four.next=Five;
ListNode head=new ListNode(1);
head.next=One;
ListNode result=findKthtotail.FindKthToTail(head,3);
System.out.println(result.val);

}
public ListNode FindKthToTail(ListNode head, int k) {
if (head == null || k <= 0)
return null;

ListNode pListNode = head, qListNode = head;

for (int i = 1; i < k; ++i) {
if (pListNode.next != null) {
pListNode = pListNode.next;
} else {
return null;
}
}

while (pListNode.next != null) {
qListNode = qListNode.next;
pListNode = pListNode.next;
}

return qListNode;

}

}