2．　　采用相邻矩阵表示一个有向图G，写一个算法确定G是否有一个漏(即入度为n-1，出度为0的顶点)，要求该算法的时间复杂度是o(n2)。-2. Using adjacency matrix represents a directed graph G, G wrote an algorithm to determine whether there is a leak (ie, the degree of n-1, a degree of a vertex is 0), the requirements of the algorithm time complexity is o (n2).