查找单链表的倒数第K个节点，要求只能遍历一遍链表

算法思想：使用快慢指针

const list_node* Find_K( list_node*& list, int K)
{
	list_node* fast_p = list;
	list_node* slow_p = list;
	for (int i = 0; i < K; i++)
	{
		fast_p = fast_p->next;
	}

	while (fast_p != NULL)
	{
		fast_p = fast_p->next;
		slow_p = slow_p->next;
	}

	return slow_p;
}