首先一次遍历计算出链表长度;然后从头开始遍历,遍历到k-i就返回(i为链表下标,从0开始)

public ListNode FindKthToTail (ListNode pHead, int k) {
        // write code here
        //先计算出长度,然后循环判断
        ListNode dummy = new ListNode(0);
        dummy.next = pHead;
        ListNode temp = pHead;
        int len = 0;
        while(temp != null){
            len++;
            temp = temp.next;
        }

        ListNode cur = dummy.next;
        int i = 0; 
        while(cur != null){
            if(k == len - i){
                return cur;
            }else{
                cur = cur.next;
                i++;
            }
        }
        return null;
    }