链表中倒数第k个结点的值

跟删除链表中倒数第n个结点做法一样，用快慢指针，只是本题需要加多一个判断，当快指针先走完的时候，证明倒数第k个结点已经超出了链表的头结点，此时直接返回null

public class Solution {
    public ListNode FindKthToTail(ListNode head,int k) {
        if(head == null)
            return head;
        ListNode pre = new ListNode(0);
        pre.next = head;
        ListNode start = pre;
        ListNode end = pre;
        while(k != 0){
            start = start.next;
            if(start == null)
                return null;
            k--;
        }
        while(start.next != null){
            start = start.next;
            end = end.next;
        }
        return end.next;
    }
}