链表中倒数最后k个结点

数组越界：
head为空指针；
k大于链表的长度；
输入的参数k为0;

public class Solution {
    public ListNode FindKthToTail (ListNode head, int k) {
        ListNode slow = head, fast = head;
        while (k-- > 0 && fast != null) fast = fast.next;
        if (k != -1) return null;
        while (fast != null) {
            slow = slow.next;
            fast = fast.next;
        }
        return slow;
    }
}