链表倒数第k个节点

question：输入一个链表，输出该链表中倒数第k个结点。

resolution:

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

        ListNode(int val) {
            this.val = val;
        }
    }   
 public ListNode FindKthToTail(ListNode head,int k) {

        if (head == null) return null;//考虑特殊情况

        int len = 1;//注意起始值
        int i = 1;//起始值不为0
        ListNode tempHead = head;
        ListNode result = null;
        while (tempHead.next != null){
            tempHead = tempHead.next;
            len++;
        }
        int index = len  - k +1;
        while (head != null){//不用head.next==null，否则遍历不到最后一个节点
            if(i == index){//先判断，再遍历和自增，注意先后顺序
                result = head;
                break;
            }
            head = head.next;
            i++;
        }
        return result;
    }