struct ListNode* FindKthToTail(struct ListNode* pListHead, int k ) 
{
    struct ListNode* slow,*fast;
    slow = fast = pListHead;
    while(k--)
    {
        if(fast==NULL)
        {
            return NULL;
        }
        fast=fast->next;
    }
    while(fast)
    {
        slow=slow->next;
        fast=fast->next;
    }
    return slow;
}