说明：  设计一个算法，按照深度优先遍历的思想找出从指定结点出发，长度为M的所有简单路径。并将此算法用于邻接表类，在邻接表类中定义一个共有成员函数find(start, m)。
(In adjlink to class with negative right value realization monosource shortest path function. Design an algorithm, according to traverse the depth first thoughts from specified node to find out, based on all of the simple length for M path. This algorithm is used for adjlink to class, defined in the class in adjlink to a mutual member function find (start, m).)