剑指offer--链表中倒数第k个结点

/*
public class ListNode {
int val;
ListNode next = null;

ListNode(int val) {
this.val = val;
}
}*/
public class Solution {
public ListNode FindKthToTail(ListNode head,int k) {
ListNode p = head;
int len = 0;
if (k < 0) {
System.out.println("k不可以为负数");
return null;
}

if (head == null) {
System.out.println("单链表为空");
return null;
}

while(p != null){
len++;
p = p.next;
}

if ( k > len){
System.out.print("单链表太短");
return null;
}else{
k = len - k ;
while(k > 0){
head = head.next;
k--;
}
return head;
}
}
}