Floyd算法的基本思想是，从邻接矩阵a开始进行n次迭代，第一次迭代后a[i,j]的值是从vi到vj且中间不经过变化大于1的顶点的最短路径长度；第k次迭代后a[i,j]的值是从vi到vj且中间不经过变化大于k的顶点的最短路径长度 第n次迭代后a[i,j]的值就是从vi到vj的最短路径长度。-Floyd algorithm for the basic idea is that from the adjacency matrix a start n iterations, after the first iteration a [i, j] values are from vi to vj and not through changes in the middle of more than 1 vertex of the shortest path length　 the first k iterations after a [i, j] values are from vi to vj and not through changes in the middle of the vertex k is greater than the shortest path length of the first n iterations, after a [i, j] value is from vi to vj of the shortest path length.