链表倒数第K个数

//思路：快慢指针
public ListNode FindKthToTail(ListNode head,int k) {
        //链表为空，或者k为0
        if(head == null || k == 0){
            return null;
        }

        ListNode slow = head;
        ListNode fast = head;

        //fast向右移动k-1步，使得fast 和slow 相差k
        for(int i = 1; i < k; i++) {
            fast = fast.next; 
        }

        //k比链表长度还大
        if(fast == null){
            return null;
        }

        while(fast.next != null) {
            fast = fast.next;
            slow = slow .next;
        }

        return slow;

    }