输入一个单向链表，输出该链表中倒数第k 个结点。链表的倒数第0 个结点为链表的尾指针。

链表结点定义如下：

struct ListNode
{
    int m_nKey;
    ListNode* m_pNext;
};

算法实现：

ListNode* FindLastK(ListNode* head, int k)
{
    ListNode* p1=head, *p2=head;
    int nNode=0;
 
    while(p1->m_pNext != NULL)
    {
        nNode++;
        p1=p1->m_pNext;
    }
 
    if(k>nNode)
        return NULL;
 
    int i=0;
    while(i <= nNode-k)
    {
        p2=p2->m_pNext;
        i++;
    }
 
    return p2;
}
 
int main()
{
    ListNode* pHeader = NULL;
    ListNode head;
    pHeader = &head;
    pHeader->m_pNext = NULL;
 
    for(int i=1; i <=5; i++)
    {
        ListNode* node = new ListNode();
        node->m_nKey = i;
        node->m_pNext = pHeader->m_pNext;
        pHeader->m_pNext = node;
    }
    ListNode* ret = FindLastK(pHeader,1);
    if(ret != NULL)
    {
        cout << "Value is " << ret->m_nKey << endl;
    }
    return 0;
}