思路：利用快慢指针空间差

代码：

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